blender
/
blender
129
398
Fork 572
Code Issues 6.2k Pull Requests 749 Projects 19 Wiki Activity

API docs: intro overhaul 

- Update terminology, spelling, formatting.
- Rename screen to workspace.
- Update for 2.8 UI changes.
This commit is contained in:
Tobias Heinke 2020-06-23 23:08:49 +10:00 committed by Campbell Barton
parent 0aa7c11788
commit 23f8ab4250
8 changed files with 638 additions and 762 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
doc/python_api/rst/bgl.rst
View File

@ -427,7 +427,7 @@ offers a set of extensive examples, including advanced features.
Return evaluator parameters
.. seealso:: `OpenGL Docs <https://www.opengl.org/sdk/docs/man2/xhtml/glGetMap.xml>`_
.. seealso:: `OpenGL Docs <https://www.opengl.org/sdk/docs/man2/xhtml/glGetMap.xml>`__
:type target: Enumerated constant
:arg target: Specifies the symbolic name of a map.

88
doc/python_api/rst/include__bmesh.rst
View File

@ -1,5 +1,5 @@
..
This document is appended to the auto generated bmesh api doc to avoid clogging up the C files with details.
This document is appended to the auto generated BMesh API doc to avoid clogging up the C files with details.
to test this run:
./blender.bin -b -noaudio -P doc/python_api/sphinx_doc_gen.py -- \
--partial bmesh* ; cd doc/python_api ; sphinx-build sphinx-in sphinx-out ; cd ../../
@ -19,25 +19,24 @@ Submodules:
Introduction
------------
This API gives access the blenders internal mesh editing api, featuring geometry connectivity data and
This API gives access the Blender's internal mesh editing API, featuring geometry connectivity data and
access to editing operations such as split, separate, collapse and dissolve.
The features exposed closely follow the C API,
giving python access to the functions used by blenders own mesh editing tools.
giving Python access to the functions used by Blender's own mesh editing tools.
For an overview of BMesh data types and how they reference each other see:
`BMesh Design Document <https://wiki.blender.org/index.php/Dev:Source/Modeling/BMesh/Design>`_ .
`BMesh Design Document <https://wiki.blender.org/index.php/Dev:Source/Modeling/BMesh/Design>`__.
.. note::
**Disk** and **Radial** data is not exposed by the python api since this is for internal use only.
**Disk** and **Radial** data is not exposed by the Python API since this is for internal use only.
.. warning:: TODO items are...
* add access to BMesh **walkers**
* add custom-data manipulation functions add/remove/rename.
- add access to BMesh **walkers**.
- add custom-data manipulation functions add, remove or rename.
Example Script
@ -46,55 +45,52 @@ Example Script
.. literalinclude:: __/__/__/release/scripts/templates_py/bmesh_simple.py
Stand-Alone Module
^^^^^^^^^^^^^^^^^^
Standalone Module
^^^^^^^^^^^^^^^^^
The bmesh module is written to be standalone except for :mod:`mathutils`
The BMesh module is written to be standalone except for :mod:`mathutils`
which is used for vertex locations and normals.
The only other exception to this are when converting mesh data to and from :class:`bpy.types.Mesh`.
Mesh Access
-----------
There are 2 ways to access BMesh data, you can create a new BMesh by converting a mesh from
:class:`bpy.types.BlendData.meshes` or by accessing the current edit mode mesh.
see: :class:`bmesh.types.BMesh.from_mesh` and :mod:`bmesh.from_edit_mesh` respectively.
There are two ways to access BMesh data, you can create a new BMesh by converting a mesh from
:class:`bpy.types.BlendData.meshes` or by accessing the current Edit-Mode mesh.
See: :class:`bmesh.types.BMesh.from_mesh` and :mod:`bmesh.from_edit_mesh` respectively.
When explicitly converting from mesh data python **owns** the data, that is to say -
that the mesh only exists while python holds a reference to it,
and the script is responsible for putting it back into a mesh data-block when the edits are done.
When explicitly converting from mesh data Python **owns** the data, that means that
the mesh only exists while Python holds a reference to it.
The script is responsible for putting it back into a mesh data-block when the edits are done.
Note that unlike :mod:`bpy`, a BMesh does not necessarily correspond to data in the currently open blend file,
Note that unlike :mod:`bpy`, a BMesh does not necessarily correspond to data in the currently open blend-file,
a BMesh can be created, edited and freed without the user ever seeing or having access to it.
Unlike edit mode, the bmesh module can use multiple BMesh instances at once.
Unlike Edit-Mode, the BMesh module can use multiple BMesh instances at once.
Take care when dealing with multiple BMesh instances since the mesh data can use a lot of memory, while a mesh that
python owns will be freed in when the script holds no references to it,
its good practice to call :class:`bmesh.types.BMesh.free` which will remove all the mesh data immediately and disable
further access.
Take care when dealing with multiple BMesh instances since the mesh data can use a lot of memory.
While a mesh that the Python script owns will be freed when the script holds no references to it,
it's good practice to call :class:`bmesh.types.BMesh.free` which will remove all the mesh data immediately
and disable further access.
EditMode Tessellation
^^^^^^^^^^^^^^^^^^^^^
Edit-Mode Tessellation
^^^^^^^^^^^^^^^^^^^^^^
When writing scripts that operate on editmode data you will normally want to re-calculate the tessellation after
running the script, this needs to be called explicitly.
The BMesh its self does not store the triangulated faces, they are stored in the :class:`bpy.types.Mesh`,
When writing scripts that operate on Edit-Mode data you will normally want to re-calculate the tessellation after
running the script, this needs to be called explicitly.
The BMesh itself does not store the triangulated faces, instead they are stored in the :class:`bpy.types.Mesh`,
to refresh tessellation triangles call :class:`bpy.types.Mesh.calc_loop_triangles`.
CustomData Access
-----------------
BMesh has a unified way to access mesh attributes such as UV's vertex colors, shape keys, edge crease etc.
BMesh has a unified way to access mesh attributes such as UVs, vertex colors, shape keys, edge crease, etc.
This works by having a **layers** property on BMesh data sequences to access the custom data layers
which can then be used to access the actual data on each vert, edge, face or loop.
This works by having a **layers** property on bmesh data sequences to access the custom data layers which can then be
used to access the actual data on each vert/edge/face/loop.
Here are some examples ...
Here are some examples:
.. code-block:: python
@ -139,27 +135,27 @@ Here are some examples ...
Keeping a Correct State
-----------------------
When modeling in blender there are certain assumptions made about the state of the mesh.
When modeling in Blender there are certain assumptions made about the state of the mesh:
* hidden geometry isn't selected.
* when an edge is selected, its vertices are selected too.
* when a face is selected, its edges and vertices are selected.
* duplicate edges / faces don't exist.
* faces have at least 3 vertices.
- Hidden geometry isn't selected.
- When an edge is selected, its vertices are selected too.
- When a face is selected, its edges and vertices are selected.
- Duplicate edges / faces don't exist.
- Faces have at least three vertices.
To give developers flexibility these conventions are not enforced,
however tools must leave the mesh in a valid state else other tools may behave incorrectly.
yet tools must leave the mesh in a valid state or else other tools may behave incorrectly.
Any errors that arise from not following these conventions is considered a bug in the script,
not a bug in blender.
not a bug in Blender.
Selection / Flushing
^^^^^^^^^^^^^^^^^^^^
As mentioned above, it is possible to create an invalid selection state
(by selecting a state and then de-selecting one of its vertices's for example), mostly the best way to solve this is to
flush the selection after performing a series of edits. this validates the selection state.
(by selecting a state and then deselecting one of its vertices for example),
mostly the best way to solve this is to flush the selection
after performing a series of edits. This validates the selection state.
Module Functions

245
doc/python_api/rst/info_api_reference.rst
View File

@ -3,94 +3,84 @@
Reference API Usage
*******************
Blender has many interlinking data types which have an auto-generated reference api which often has the information
Blender has many interlinking data types which have an auto-generated reference API which often has the information
you need to write a script, but can be difficult to use.
This document is designed to help you understand how to use the reference api.
This document is designed to help you understand how to use the reference API.
Reference API Scope
===================
The reference API covers :mod:`bpy.types`, which stores types accessed via :mod:`bpy.context` - *The user context*
or :mod:`bpy.data` - *Blend file data*.
The reference API covers :mod:`bpy.types`, which stores types accessed via :mod:`bpy.context` -- *the user context*
or :mod:`bpy.data` -- *blend-file data*.
Other modules such as :mod:`bmesh` and :mod:`aud` are not using Blenders data API
Other modules such as :mod:`bmesh` and :mod:`aud` are not using Blender's data API
so this document doesn't apply to those modules.
Data Access
===========
The most common case for using the reference API is to find out how to access data in the blend file.
Before going any further its best to be aware of ID Data-Blocks in Blender since you will often find properties
The most common case for using the reference API is to find out how to access data in the blend-file.
Before going any further its best to be aware of ID data-blocks in Blender since you will often find properties
relative to them.
ID Data
-------
ID Data-Blocks are used in Blender as top-level data containers.
ID data-blocks are used in Blender as top-level data containers.
From the user interface this isn't so obvious, but when developing you need to know about ID data-blocks.
ID data types include Scene, Group, Object, Mesh, Workspace, World, Armature, Image and Texture.
For a full list see the subclasses of :class:`bpy.types.ID`.
From the user interface this isn't so obvious, but when developing you need to know about ID Data-Blocks.
Here are some characteristics ID data-blocks share:
ID data types include Scene, Group, Object, Mesh, Screen, World, Armature, Image and Texture.
for a full list see the sub-classes of :class:`bpy.types.ID`
Here are some characteristics ID Data-Blocks share.
- ID's are blend file data, so loading a new blend file reloads an entire new set of Data-Blocks.
- ID's can be accessed in Python from ``bpy.data.*``
- IDs are blend-file data, so loading a new blend-file reloads an entire new set of data-blocks.
- IDs can be accessed in Python from ``bpy.data.*``.
- Each data-block has a unique ``.name`` attribute, displayed in the interface.
- Animation data is stored in ID's ``.animation_data``.
- ID's are the only data types that can be linked between blend files.
- ID's can be added/copied and removed via Python.
- ID's have their own garbage-collection system which frees unused ID's when saving.
- When a data-block has a reference to some external data, this is typically an ID Data-Block.
- Animation data is stored in IDs ``.animation_data``.
- IDs are the only data types that can be linked between blend-files.
- IDs can be added/copied and removed via Python.
- IDs have their own garbage-collection system which frees unused IDs when saving.
- When a data-block has a reference to some external data, this is typically an ID data-block.
Simple Data Access
------------------
Lets start with a simple case, say you want a python script to adjust the object's location.
In this simple case a Python script is used to adjust the object's location.
Start by collecting the information where the data is located.
Start by finding this setting in the interface ``Properties Window -> Object -> Transform -> Location``
From the button you can right click and select **Online Python Reference**, this will link you to:
:class:`bpy.types.Object.location`
Being an API reference, this link often gives little more information then the tool-tip, though some of the pages
First find this setting in the interface ``Properties editor -> Object -> Transform -> Location``.
From the button context menu select *Online Python Reference*, this will link you to:
:class:`bpy.types.Object.location`.
Being an API reference, this link often gives little more information then the tooltip, though some of the pages
include examples (normally at the top of the page).
But you now know that you have to use ``.location`` and that its an array of three floats.
At this point you may say *Now what?* - you know that you have to use ``.location`` and that its an array of 3 floats
but you're still left wondering how to access this in a script.
So the next step is to find out where to access objects, go down to the bottom of the page to the **References**
section, for objects there are many references, but one of the most common places to access objects is via the context.
It's easy to be overwhelmed at this point since there ``Object`` get referenced in so many places - modifiers,
functions, textures and constraints.
So the next step is to find out where to access objects, go down to the bottom of the page to the references section,
for objects there are many references, but one of the most common places to access objects is via the context.
It's easy to be overwhelmed at this point since there ``Object`` get referenced in so many places:
modifiers, functions, textures and constraints.
But if you want to access any data the user has selected
you typically only need to check the :mod:`bpy.context` references.
Even then, in this case there are quite a few though if you read over these - most are mode specific.
If you happen to be writing a tool that only runs in weight paint mode, then using ``weight_paint_object``
would be appropriate.
However to access an item the user last selected, look for the ``active`` members,
Having access to a single active member the user selects is a convention in Blender: eg. ``active_bone``,
``active_pose_bone``, ``active_node`` ... and in this case we can use - ``active_object``.
Even then, in this case there are quite a few though
if you read over these you'll notice that most are mode specific.
If you happen to be writing a tool that only runs in Weight Paint Mode,
then using ``weight_paint_object`` would be appropriate.
However, to access an item the user last selected, look for the ``active`` members,
Having access to a single active member the user selects is a convention in Blender:
e.g. ``active_bone``, ``active_pose_bone``, ``active_node``, etc. and in this case you can use ``active_object``.
So now we have enough information to find the location of the active object.
So now you have enough information to find the location of the active object.
.. code-block:: python
bpy.context.active_object.location
You can type this into the python console to see the result.
You can type this into the Python console to see the result.
The other common place to access objects in the reference is :class:`bpy.types.BlendData.objects`.
.. note::
@ -100,7 +90,7 @@ The other common place to access objects in the reference is :class:`bpy.types.B
so the documentation points there.
With :mod:`bpy.data.objects`, this is a collection of objects so you need to access one of its members.
With :mod:`bpy.data.objects`, this is a collection of objects so you need to access one of its members:
.. code-block:: python
@ -117,37 +107,34 @@ Here are some more complex examples:
.. code-block:: python
# access a render layers samples
bpy.context.scene.render.layers["RenderLayer"].samples
# Access the number of samples for the Cycles render engine.
bpy.context.scene.cycles.samples
# access to the current weight paint brush size
# Access to the current weight paint brush size.
bpy.context.tool_settings.weight_paint.brush.size
# check if the window is fullscreen
# Check if the window is full-screen.
bpy.context.window.screen.show_fullscreen
As you can see there are times when you want to access data which is nested
in a way that causes you to go through a few indirections.
The properties are arranged to match how data is stored internally (in Blender's C code) which is often logical
but not always quite what you would expect from using Blender.
So this takes some time to learn, it helps you understand how data fits together in Blender
which is important to know when writing scripts.
The properties are arranged to match how data is stored internally (in blenders C code) which is often logical but
not always quite what you would expect from using Blender.
So this takes some time to learn, it helps you understand how data fits together in Blender which is important
to know when writing scripts.
When starting out scripting you will often run into the problem where you're not sure how to access the data you want.
There are a few ways to do this.
When starting out scripting you will often run into the problem
where you're not sure how to access the data you want.
There are a few ways to do this:
- Use the Python console's auto-complete to inspect properties.
*This can be hit-and-miss but has the advantage
that you can easily see the values of properties and assign them to interactively see the results.*
- Copy the Data-Path from the user interface.
*Explained further in :ref:`Copy Data Path <info_data_path_copy>`*
- Copy the data path from the user interface.
*Explained further in* :ref:`Copy Data Path <info_data_path_copy>`.
- Using the documentation to follow references.
*Explained further in :ref:`Indirect Data Access <info_data_path_indirect>`*
*Explained further in* :ref:`Indirect Data Access <info_data_path_indirect>`.
.. _info_data_path_copy:
@ -155,42 +142,36 @@ There are a few ways to do this.
Copy Data Path
--------------
Blender can compute the Python string to a property which is shown in the tool-tip, on the line below ``Python: ...``,
This saves having to use the API reference to click back up the references to find where data is accessed from.
There is a user-interface feature to copy the data-path which gives the path from an :class:`bpy.types.ID` data-block,
Blender can compute the Python string to a property which is shown in the tooltip,
on the line below ``Python: ...``. This saves having to open the API references to find where data is accessed from.
In the context menu is a copy data-path tool which gives the path from an :class:`bpy.types.ID` data-block,
to its property.
To see how this works we'll get the path to the Subdivision-Surface modifiers subdivision setting.
Start with the default scene and select the **Modifiers** tab, then add a **Subdivision-Surface** modifier to the cube.
Now hover your mouse over the button labeled **View**, The tool-tip includes :class:`bpy.types.SubsurfModifier.levels`
but we want the path from the object to this property.
To see how this works you'll get the path to the Subdivision Surface modifiers *Levels* setting.
Start with the default scene and select the Modifiers tab, then add a Subdivision Surface modifier to the cube.
Now hover your mouse over the button labeled *Levels Viewport*,
The tooltip includes :class:`bpy.types.SubsurfModifier.levels` but you want the path from the object to this property.
Note that the text copied won't include the ``bpy.data.collection["name"].`` component since its assumed that
you won't be doing collection look-ups on every access and typically you'll want to use the context rather
then access each :class:`bpy.types.ID` instance by name.
Type in the ID path into a Python console :mod:`bpy.context.active_object`.
Include the trailing dot and don't hit "enter", yet.
Include the trailing dot and don't execute the code, yet.
Now right-click on the button and select **Copy Data Path**, then paste the result into the console.
So now you should have the answer:
Now in the button's context menu select *Copy Data Path*, then paste the result into the console:
.. code-block:: python
bpy.context.active_object.modifiers["Subsurf"].levels
Hit "enter" and you'll get the current value of 1. Now try changing the value to 2:
Press :kbd:`Return` and you'll get the current value of 1. Now try changing the value to 2:
.. code-block:: python
bpy.context.active_object.modifiers["Subsurf"].levels = 2
bpy.context.active_object.modifiers["Subsurf"].levels = 2
You can see the value update in the Subdivision-Surface modifier's UI as well as the cube.
You can see the value update in the Subdivision Surface modifier's UI as well as the cube.
.. _info_data_path_indirect:
@ -198,51 +179,45 @@ You can see the value update in the Subdivision-Surface modifier's UI as well as
Indirect Data Access
--------------------
For this example we'll go over something more involved, showing the steps to access the active sculpt brushes texture.
This more advanced example shows the steps to access the active sculpt brushes texture.
For example, if you want to access the texture of a brush via Python to adjust its ``contrast``.
Lets say we want to access the texture of a brush via Python, to adjust its ``contrast`` for example.
#. Start in the default scene and enable Sculpt Mode from the 3D Viewport header.
#. From the Sidebar expand the Brush Settings panel's *Texture* subpanel and add a new texture.
*Notice the texture data-block menu itself doesn't have very useful links (you can check the tooltips).*
#. The contrast setting isn't exposed in the Sidebar, so view the texture in the properties editor:
- Start in the default scene and enable 'Sculpt' mode from the 3D-View header.
- From the toolbar expand the **Texture** panel and add a new texture.
*Notice the texture button its self doesn't have very useful links (you can check the tooltips).*
- The contrast setting isn't exposed in the sculpt toolbar, so view the texture in the properties panel...
- In the properties editor select the Texture tab.
- Select brush texture.
- Expand the *Colors* panel to locate the *Contrast* number field.
#. Open the context menu of the contrast field and select *Online Python Reference*.
This takes you to ``bpy.types.Texture.contrast``. Now you can see that ``contrast`` is a property of texture.
#. To find out how to access the texture from the brush check on the references at the bottom of the page.
Sometimes there are many references, and it may take some guesswork to find the right one,
but in this case it's ``Brush.texture``.
- In the properties button select the Texture context.
- Select the Brush icon to show the brush texture.
- Expand the *Colors* panel to locate the *Contrast* button.
- Right click on the contrast button and select **Online Python Reference**
This takes you to ``bpy.types.Texture.contrast``
- Now we can see that ``contrast`` is a property of texture,
so next we'll check on how to access the texture from the brush.
- Check on the **References** at the bottom of the page, sometimes there are many references, and it may take
some guess work to find the right one, but in this case its obviously ``Brush.texture``.
#. Now you know that the texture can be accessed from ``bpy.data.brushes["BrushName"].texture``
but normally you *won't* want to access the brush by name, instead you want to access the active brush.
So the next step is to check on where brushes are accessed from via the references.
In this case there it is simply ``bpy.context.brush``.
*Now we know that the texture can be accessed from* ``bpy.data.brushes["BrushName"].texture``
*but normally you won't want to access the brush by name, so we'll see now to access the active brush instead.*
- So the next step is to check on where brushes are accessed from via the **References**.
In this case there is simply ``bpy.context.brush`` which is all we need.
Now you can use the Python console to form the nested properties needed to access brush textures contrast:
*Context -> Brush -> Texture -> Contrast*.
Now you can use the Python console to form the nested properties needed to access brush textures contrast,
logically we now know.
*Context -> Brush -> Texture -> Contrast*
Since the attribute for each is given along the way we can compose the data path in the python console:
Since the attribute for each is given along the way you can compose the data path in the Python console:
.. code-block:: python
bpy.context.brush.texture.contrast
There can be multiple ways to access the same data, which you choose often depends on the task.
An alternate path to access the same setting is...
An alternate path to access the same setting is:
.. code-block:: python
bpy.context.sculpt.brush.texture.contrast
Or access the brush directly...
Or access the brush directly:
.. code-block:: python
@ -251,27 +226,24 @@ Or access the brush directly...
If you are writing a user tool normally you want to use the :mod:`bpy.context` since the user normally expects
the tool to operate on what they have selected.
For automation you are more likely to use :mod:`bpy.data` since you want to be able to access specific data and manipulate
it, no matter what the user currently has the view set at.
For automation you are more likely to use :mod:`bpy.data` since you want to be able to access specific data and
manipulate it, no matter what the user currently has the view set at.
Operators
=========
Most key-strokes and buttons in Blender call an operator which is also exposed to python via :mod:`bpy.ops`,
Most hotkeys and buttons in Blender call an operator which is also exposed to Python via :mod:`bpy.ops`.
To see the Python equivalent hover your mouse over the button and see the tool-tip,
eg ``Python: bpy.ops.render.render()``,
If there is no tool-tip or the ``Python:`` line is missing then this button is not using an operator and
can't be accessed from Python.
To see the Python equivalent hover your mouse over the button and see the tooltip,
e.g ``Python: bpy.ops.render.render()``,
If there is no tooltip or the ``Python:`` line is missing then this button is not using an operator
and can't be accessed from Python.
If you want to use this in a script you can press :kbd:`Control-C` while your mouse is over the button to copy it to the
clipboard.
You can also right click on the button and view the **Online Python Reference**, this mainly shows arguments and
their defaults however operators written in Python show their file and line number which may be useful if you
If you want to use this in a script you can press :kbd:`Ctrl-C` while your mouse is over the button
to copy it to the clipboard.
You can also use button's context menu and view the *Online Python Reference*, this mainly shows arguments and
their defaults, however, operators written in Python show their file and line number which may be useful if you
are interested to check on the source code.
.. note::
@ -280,21 +252,18 @@ are interested to check on the source code.
for more on this see :ref:`using operators <using_operators>`.
Info View
---------
Info Editor
-----------
Blender records operators you run and displays them in the **Info** space.
This is located above the file-menu which can be dragged down to display its contents.
Blender records operators you run and displays them in the Info editor.
Select the Scripting workspace that comes default with Blender to see its output.
You can perform some actions and see them show up -- delete a vertex for example.
Select the **Script** screen that comes default with Blender to see its output.
You can perform some actions and see them show up - delete a vertex for example.
Each entry can be selected (Right-Mouse-Button),
then copied :kbd:`Control-C`, usually to paste in the text editor or python console.
Each entry can be selected, then copied :kbd:`Ctrl-C`, usually to paste in the text editor or Python console.
.. note::
Not all operators get registered for display,
zooming the view for example isn't so useful to repeat so its excluded from the output.
To display *every* operator that runs see :ref:`Show All Operators <info_show_all_operators>`
To display *every* operator that runs see :ref:`Show All Operators <info_show_all_operators>`.

259
doc/python_api/rst/info_best_practice.rst
View File

@ -3,38 +3,34 @@
Best Practice
*************
When writing your own scripts python is great for new developers to pick up and become productive,
but you can also pick up odd habits or at least write scripts that are not easy for others to understand.
When writing your own scripts Python is great for new developers to pick up and become productive,
but you can also pick up bad practices or at least write scripts that are not easy for others to understand.
For your own work this is of course fine,
but if you want to collaborate with others or have your work included with blender there are practices we encourage.
but if you want to collaborate with others or have your work included with Blender there are practices we encourage.
Style Conventions
=================
For Blender/Python development we have chosen to follow python suggested style guide to avoid mixing styles
amongst our own scripts and make it easier to use python scripts from other projects.
For Blender Python development we have chosen to follow Python suggested style guide to avoid mixing styles
among our own scripts and make it easier to use Python scripts from other projects.
Using our style guide for your own scripts makes it easier if you eventually want to contribute them to Blender.
Using our style guide for your own scripts makes it easier if you eventually want to contribute them to blender.
This style guide is known as `pep8 <https://www.python.org/dev/peps/pep-0008/>`__
and here is a brief listing of pep8 criteria:
This style guide is known as pep8 and can be found `here <https://www.python.org/dev/peps/pep-0008/>`_
- Camel caps for class names: MyClass
- All lower case underscore separated module names: my_module
- Indentation of 4 spaces (no tabs)
- Spaces around operators: ``1 + 1``, not ``1+1``
- Only use explicit imports (no wildcard importing ``*``)
- Don't use multiple statements on a single line: ``if val: body``, separate onto two lines instead.
A brief listing of pep8 criteria.
- camel caps for class names: MyClass
- all lower case underscore separated module names: my_module
- indentation of 4 spaces (no tabs)
- spaces around operators. ``1 + 1``, not ``1+1``
- only use explicit imports, (no importing ``*``)
- don't use single line: ``if val: body``, separate onto 2 lines instead.
As well as pep8 we have other conventions used for blender python scripts.
As well as pep8 we have additional conventions used for Blender Python scripts:
- Use single quotes for enums, and double quotes for strings.
Both are of course strings, but in our internal API enums are unique items from a limited set. eg.
Both are of course strings, but in our internal API enums are unique items from a limited set, e.g:
.. code-block:: python
@ -42,14 +38,14 @@ As well as pep8 we have other conventions used for blender python scripts.
bpy.context.scene.render.filepath = "//render_out"
- pep8 also defines that lines should not exceed 79 characters,
we felt this is too restrictive so this is optional per script.
we have decided that this is too restrictive so it is optional per script.
Periodically we run checks for pep8 compliance on blender scripts,
for scripts to be included in this check add this line as a comment at the top of the script.
Periodically we run checks for pep8 compliance on Blender scripts,
for scripts to be included in this check add this line as a comment at the top of the script:
``# <pep8 compliant>``
To enable line length checks use this instead.
To enable line length checks use this instead:
``# <pep8-80 compliant>``
@ -59,85 +55,79 @@ User Interface Layout
Some notes to keep in mind when writing UI layouts:
- UI code is quite simple. Layout declarations are there to easily create a decent layout.
UI code is quite simple. Layout declarations are there to easily create a decent layout.
The general rule here is: If you need more code for the layout declaration,
than for the actual properties, then you are doing it wrong.
General rule here: If you need more code for the layout declaration,
then for the actual properties, you do it wrong.
Example layouts:
.. rubric:: Example layouts:
- layout()
``layout()``
The basic layout is a simple top-to-bottom layout.
The basic layout is a simple Top -> Bottom layout.
.. code-block:: python
.. code-block:: python
layout.prop()
layout.prop()
layout.prop()
layout.prop()
``layout.row()``
Use ``row()``, when you want more than one property in a single line.
- layout.row()
.. code-block:: python
Use row(), when you want more than 1 property in one line.
row = layout.row()
row.prop()
row.prop()
.. code-block:: python
``layout.column()``
Use ``column()``, when you want your properties in a column.
row = layout.row()
row.prop()
row.prop()
.. code-block:: python
- layout.column()
col = layout.column()
col.prop()
col.prop()
Use column(), when you want your properties in a column.
``layout.split()``
This can be used to create more complex layouts.
For example, you can split the layout and create two ``column()`` layouts next to each other.
Do not use split, when you simply want two properties in a row. Use ``row()`` instead.
.. code-block:: python
.. code-block:: python
col = layout.column()
col.prop()
col.prop()
split = layout.split()
- layout.split()
col = split.column()
col.prop()
col.prop()
This can be used to create more complex layouts.
For example you can split the layout and create two column() layouts next to each other.
Don't use split, when you simply want two properties in a row. Use row() for that.
col = split.column()
col.prop()
col.prop()
.. code-block:: python
split = layout.split()
col = split.column()
col.prop()
col.prop()
col = split.column()
col.prop()
col.prop()
Declaration names:
.. rubric:: Declaration names:
Try to only use these variable names for layout declarations:
- row for a row() layout
- col for a column() layout
- split for a split() layout
- flow for a column_flow() layout
- sub for a sub layout (a column inside a column for example)
:row: for a ``row()`` layout
:col: for a ``column()`` layout
:split: for a ``split()`` layout
:flow: for a ``column_flow()`` layout
:sub: for a sub layout (a column inside a column for example)
Script Efficiency
=================
List Manipulation (General Python Tips)
---------------------------------------
Searching for list items
Searching for List Items
^^^^^^^^^^^^^^^^^^^^^^^^
In Python there are some handy list functions that save you having to search through the list.
Even though you are not looping on the list data **python is**,
Even though you are not looping on the list data **Python is**,
so you need to be aware of functions that will slow down your script by searching the whole list.
.. code-block:: python
@ -150,23 +140,21 @@ so you need to be aware of functions that will slow down your script by searchin
Modifying Lists
^^^^^^^^^^^^^^^
In python we can add and remove from a list, this is slower when the list length is modified,
especially at the start of the list, since all the data after the index of
modification needs to be moved up or down 1 place.
The most simple way to add onto the end of the list is to use
``my_list.append(list_item)`` or ``my_list.extend(some_list)`` and the fastest way to
remove an item is ``my_list.pop()`` or ``del my_list[-1]``.
In Python you can add and remove from a list, this is slower when the list length is modified,
especially at the start of the list, since all the data after the index of
modification needs to be moved up or down one place.
The fastest way to add onto the end of the list is to use
``my_list.append(list_item)`` or ``my_list.extend(some_list)`` and
to remove an item is ``my_list.pop()`` or ``del my_list[-1]``.
To use an index you can use ``my_list.insert(index, list_item)`` or ``list.pop(index)``
for list removal, but these are slower.
Sometimes its faster (but more memory hungry) to just rebuild the list.
Say you want to remove all triangular polygons in a list.
Rather than...
Sometimes it's faster (but less memory efficient) to just rebuild the list.
For example if you want to remove all triangular polygons in a list.
Rather than:
.. code-block:: python
@ -179,7 +167,7 @@ Rather than...
polygons.pop(p_idx) # remove the triangle
It's faster to build a new list with list comprehension.
It's faster to build a new list with list comprehension:
.. code-block:: python
@ -189,14 +177,14 @@ It's faster to build a new list with list comprehension.
Adding List Items
^^^^^^^^^^^^^^^^^
If you have a list that you want to add onto another list, rather than...
If you have a list that you want to add onto another list, rather than:
.. code-block:: python
for l in some_list:
my_list.append(l)
Use...
Use:
.. code-block:: python
@ -205,9 +193,7 @@ Use...
Note that insert can be used when needed,
but it is slower than append especially when inserting at the start of a long list.
This example shows a very sub-optimal way of making a reversed list.
This example shows a very suboptimal way of making a reversed list:
.. code-block:: python
@ -219,7 +205,6 @@ This example shows a very sub-optimal way of making a reversed list.
Python provides more convenient ways to reverse a list using the slice method,
but you may want to time this before relying on it too much:
.. code-block:: python
some_reversed_list = some_list[::-1]
@ -228,12 +213,10 @@ but you may want to time this before relying on it too much:
Removing List Items
^^^^^^^^^^^^^^^^^^^
Use ``my_list.pop(index)`` rather than ``my_list.remove(list_item)``
Use ``my_list.pop(index)`` rather than ``my_list.remove(list_item)``.
This requires you to have the index of the list item but is faster since ``remove()`` will search the list.
Here is an example of how to remove items in 1 loop,
removing the last items first, which is faster (as explained above).
Here is an example of how to remove items in one loop,
removing the last items first, which is faster (as explained above):
.. code-block:: python
@ -247,7 +230,7 @@ removing the last items first, which is faster (as explained above).
This example shows a fast way of removing items,
for use in cases where you can alter the list order without breaking the scripts functionality.
This works by swapping 2 list items, so the item you remove is always last.
This works by swapping two list items, so the item you remove is always last:
.. code-block:: python
@ -260,64 +243,59 @@ This works by swapping 2 list items, so the item you remove is always last.
my_list.pop()
When removing many items in a large list this can provide a good speedup.
When removing many items in a large list this can provide a good speed-up.
Avoid Copying Lists
^^^^^^^^^^^^^^^^^^^
When passing a list/dictionary to a function,
When passing a list or dictionary to a function,
it is faster to have the function modify the list rather than returning
a new list so python doesn't have to duplicate the list in memory.
a new list so Python doesn't have to duplicate the list in memory.
Functions that modify a list in-place are more efficient than functions that create new lists.
This is generally slower so only use for functions when it makes sense not to modify the list in place.
This is generally slower so only use for functions when it makes sense not to modify the list in place:
>>> my_list = some_list_func(my_list)
This is generally faster since there is no re-assignment and no list duplication.
This is generally faster since there is no re-assignment and no list duplication:
>>> some_list_func(vec)
Also note that passing a sliced list makes a copy of the list in python memory.
Also note that, passing a sliced list makes a copy of the list in Python memory:
>>> foobar(my_list[:])
If my_list was a large array containing 10000's of items, a copy could use a lot of extra memory.
If my_list was a large array containing 10,000's of items, a copy could use a lot of extra memory.
Writing Strings to a File (Python General)
------------------------------------------
Here are 3 ways of joining multiple strings into one string for writing.
This also applies to any area of your code that involves a lot of string joining.
Here are three ways of joining multiple strings into one string for writing.
This also applies to any area of your code that involves a lot of string joining:
String concatenation
This is the slowest option, do **not** use if you can avoid it, especially when writing data in a loop.
>>> file.write(str1 + " " + str2 + " " + str3 + "\n")
String formatting
Use this when you are writing string data from floats and ints.
>>> file.write("%s %s %s\n" % (str1, str2, str3))
String joining
Use to join a list of strings (the list may be temporary). In the following example, the strings are joined with
a space " " in between, other examples are "" or ", ".
>>> file.write(" ".join((str1, str2, str3, "\n")))
``String addition`` -
this is the slowest option, *don't use if you can help it, especially when writing data in a loop*.
>>> file.write(str1 + " " + str2 + " " + str3 + "\n")
``String formatting`` -
use this when you are writing string data from floats and ints.
>>> file.write("%s %s %s\n" % (str1, str2, str3))
``String join() function``
use to join a list of strings (the list may be temporary). In the following example, the strings are joined with a space " " in between, other examples are "" or ", ".
>>> file.write(" ".join([str1, str2, str3, "\n"]))
Join is fastest on many strings,
`string formatting <https://wiki.blender.org/index.php/Dev:Source/Modeling/BMesh/Design>`__
is quite fast too (better for converting data types). String arithmetic is slowest.
Join is fastest on many strings, string formatting is quite fast too (better for converting data types).
String concatenation is the slowest.
Parsing Strings (Import/Exporting)
@ -333,36 +311,35 @@ Parsing Numbers
^^^^^^^^^^^^^^^
Use ``float(string)`` rather than ``eval(string)``, if you know the value will be an int then ``int(string)``,
float() will work for an int too but it is faster to read ints with int().
``float()`` will work for an int too but it is faster to read ints with ``int()``.
Checking String Start/End
^^^^^^^^^^^^^^^^^^^^^^^^^
If you are checking the start of a string for a keyword, rather than...
If you are checking the start of a string for a keyword, rather than:
>>> if line[0:5] == "vert ": ...
use...
Use:
>>> if line.startswith("vert "):
Using ``startswith()`` is slightly faster (approx 5%) and also avoids a possible
error with the slice length not matching the string length.
Using ``startswith()`` is slightly faster (around 5%) and also avoids a possible error
with the slice length not matching the string length.
my_string.endswith("foo_bar") can be used for line endings too.
``my_string.endswith("foo_bar")`` can be used for line endings too.
If you are unsure whether the text is upper or lower case, use the ``lower()`` or ``upper()`` string function.
If you are unsure whether the text is upper or lower case, use the ``lower()`` or ``upper()`` string function:
>>> if line.lower().startswith("vert ")
Use try/except Sparingly
------------------------
Error Handling
--------------
The **try** statement is useful to save time writing error checking code.
However **try** is significantly slower than an **if** since an exception has to be set each time,
However, **try** is significantly slower than an **if** since an exception has to be set each time,
so avoid using **try** in areas of your code that execute in a loop and runs many times.
There are cases where using **try** is faster than checking whether the condition will raise an error,
@ -382,7 +359,7 @@ In cases where you know you are checking for the same value which is referenced
Time Your Code
--------------
While developing a script it is good to time it to be aware of any changes in performance, this can be done simply.
While developing a script it is good to time it to be aware of any changes in performance, this can be done simply:
.. code-block:: python
@ -391,4 +368,4 @@ While developing a script it is good to time it to be aware of any changes in pe
# do something...
print("My Script Finished: %.4f sec" % (time.time() - time_start))
print("My Script Finished: {:.4f} sec".format(time.time() - time_start))

360
doc/python_api/rst/info_gotcha.rst
View File

@ -4,7 +4,7 @@ Gotchas
*******
This document attempts to help you work with the Blender API in areas
that can be troublesome and avoid practices that are known to give instability.
that can be troublesome and avoid practices that are known to cause instability.
.. _using_operators:
@ -12,13 +12,13 @@ that can be troublesome and avoid practices that are known to give instability.
Using Operators
===============
Blender's operators are tools for users to access, that Python can access them too is very useful
nevertheless operators have limitations that can make them cumbersome to script.
Blender's operators are tools for users to access, that can access with Python too which is very useful.
Still operators have limitations that can make them cumbersome to script.
Main limits are...
The main limits are:
- Can't pass data such as objects, meshes or materials to operate on (operators use the context instead)
- The return value from calling an operator gives the success (if it finished or was canceled),
- Can't pass data such as objects, meshes or materials to operate on (operators use the context instead).
- The return value from calling an operator is the success (if it finished or was canceled),
in some cases it would be more logical from an API perspective to return the result of the operation.
- Operators poll function can fail where an API function would raise an exception giving details on exactly why.
@ -34,26 +34,23 @@ When calling an operator gives an error like this:
Which raises the question as to what the correct context might be?
Typically operators check for the active area type, a selection or active object they can operate on,
but some operators are more picky about when they run.
but some operators are more strict when they run.
In most cases you can figure out what context an operator needs
simply be seeing how it's used in Blender and thinking about what it does.
Unfortunately if you're still stuck - the only way to **really** know
what's going on is to read the source code for the poll function and see what its checking.
by examining how it's used in Blender and thinking about what it does.
If you're still stuck, unfortunately, the only way to eventually know what is causing the error is
to read the source code for the poll function and see what it is checking.
For Python operators it's not so hard to find the source
since it's included with Blender and the source file/line is included in the operator reference docs.
since it's included with Blender and the source file and line is included in the operator reference docs.
Downloading and searching the C code isn't so simple,
especially if you're not familiar with the C language but by searching the
operator name or description you should be able to find the poll function with no knowledge of C.
especially if you're not familiar with the C language but by searching the operator name or description
you should be able to find the poll function with no knowledge of C.
.. note::
Blender does have the functionality for poll functions to describe why they fail,
but its currently not used much, if you're interested to help improve our API
feel free to add calls to ``CTX_wm_operator_poll_msg_set`` where its not obvious why poll fails.
but its currently not used much, if you're interested to help improve the API
feel free to add calls to ``CTX_wm_operator_poll_msg_set`` where its not obvious why poll fails, e.g:
>>> bpy.ops.gpencil.draw()
RuntimeError: Operator bpy.ops.gpencil.draw.poll() Failed to find Grease Pencil data to draw into
@ -63,7 +60,7 @@ The operator still doesn't work!
--------------------------------
Certain operators in Blender are only intended for use in a specific context,
some operators for example are only called from the properties window where they check the current material,
some operators for example are only called from the properties editor where they check the current material,
modifier or constraint.
Examples of this are:
@ -74,8 +71,8 @@ Examples of this are:
- :mod:`bpy.ops.buttons.file_browse`
Another possibility is that you are the first person to attempt to use this operator
in a script and some modifications need to be made to the operator to run in a different context,
if the operator should logically be able to run but fails when accessed from a script
in a script and some modifications need to be made to the operator to run in a different context.
If the operator should logically be able to run but fails when accessed from a script
it should be reported to the bug tracker.
@ -85,22 +82,20 @@ Stale Data
No updates after setting values
-------------------------------
Sometimes you want to modify values from Python and immediately access the updated values, eg:
Sometimes you want to modify values from Python and immediately access the updated values, e.g:
Once changing the objects :class:`bpy.types.Object.location`
you may want to access its transformation right after from :class:`bpy.types.Object.matrix_world`,
but this doesn't work as you might expect.
Consider the calculations that might go into working out the object's final transformation, this includes:
Consider the calculations that might contribute to the object's final transformation, this includes:
- animation function curves.
- drivers and their Python expressions.
- constraints
- parent objects and all of their f-curves, constraints etc.
- Animation function curves.
- Drivers and their Python expressions.
- Constraints
- Parent objects and all of their F-curves, constraints, etc.
To avoid expensive recalculations every time a property is modified,
Blender defers making the actual calculations until they are needed.
Blender defers the evaluation until the results are needed.
However, while the script runs you may want to access the updated values.
In this case you need to call :class:`bpy.types.ViewLayer.update` after modifying values, for example:
@ -110,44 +105,41 @@ In this case you need to call :class:`bpy.types.ViewLayer.update` after modifyin
bpy.context.view_layer.update()
Now all dependent data (child objects, modifiers, drivers... etc)
Now all dependent data (child objects, modifiers, drivers, etc.)
has been recalculated and is available to the script within active view layer.
Can I redraw during the script?
-------------------------------
Can I redraw during script execution?
-------------------------------------
The official answer to this is no, or... *"You don't want to do that"*.
To give some background on the topic...
To give some background on the topic:
While a script executes Blender waits for it to finish and is effectively locked until its done,
while in this state Blender won't redraw or respond to user input.
Normally this is not such a problem because scripts distributed with Blender
tend not to run for an extended period of time,
nevertheless scripts *can* take ages to execute and its nice to see what's going on in the view port.
nevertheless scripts *can* take a long time to complete and it would be nice to see progress in the viewport.
Tools that lock Blender in a loop and redraw are highly discouraged
since they conflict with Blenders ability to run multiple operators
When tools lock Blender in a loop redraw are highly discouraged
since they conflict with Blender's ability to run multiple operators
at once and update different parts of the interface as the tool runs.
So the solution here is to write a **modal** operator, that is - an operator which defines a modal() function,
See the modal operator template in the text editor.
So the solution here is to write a **modal** operator, which is an operator that defines a ``modal()`` function,
See the modal operator template in the text editor.
Modal operators execute on user input or setup their own timers to run frequently,
they can handle the events or pass through to be handled by the keymap or other modal operators.
Transform, Painting, Fly-Mode and File-Select are example of a modal operators.
Examples of a modal operators are Transform, Painting, Fly Navigation and File Select.
Writing modal operators takes more effort than a simple ``for`` loop
that happens to redraw but is more flexible and integrates better with Blenders design.
that contains draw calls but is more flexible and integrates better with Blender's design.
**Ok, Ok! I still want to draw from Python**
.. rubric:: Ok, Ok! I still want to draw from Python
If you insist - yes its possible, but scripts that use this hack won't be considered
for inclusion in Blender and any issues with using it won't be considered bugs,
this is also not guaranteed to work in future releases.
If you insist -- yes it's possible, but scripts that use this hack will not be considered
for inclusion in Blender and any issue with using it will not be considered a bug,
there is also no guaranteed compatibility in future releases.
.. code-block:: python
@ -157,18 +149,18 @@ this is also not guaranteed to work in future releases.
Modes and Mesh Access
=====================
When working with mesh data you may run into the problem where a script fails to run as expected in edit-mode.
This is caused by edit-mode having its own data which is only written back to the mesh when exiting edit-mode.
When working with mesh data you may run into the problem where a script fails to run as expected in Edit-Mode.
This is caused by Edit-Mode having its own data which is only written back to the mesh when exiting Edit-Mode.
A common example is that exporters may access a mesh through ``obj.data`` (a :class:`bpy.types.Mesh`)
but the user is in edit-mode, where the mesh data is available but out of sync with the edit mesh.
when the user is in Edit-Mode, where the mesh data is available but out of sync with the edit mesh.
In this situation you can...
- Exit edit-mode before running the tool.
- Exit Edit-Mode before running the tool.
- Explicitly update the mesh by calling :class:`bmesh.types.BMesh.to_mesh`.
- Modify the script to support working on the edit-mode data directly, see: :mod:`bmesh.from_edit_mesh`.
- Report the context as incorrect and only allow the script to run outside edit-mode.
- Report the context as incorrect and only allow the script to run outside Edit-Mode.
.. _info_gotcha_mesh_faces:
@ -176,24 +168,24 @@ In this situation you can...
N-Gons and Tessellation
=======================
Since 2.63 NGons are supported, this adds some complexity
Since 2.63 n-gons are supported, this adds some complexity
since in some cases you need to access triangles still (some exporters for example).
There are now 3 ways to access faces:
There are now three ways to access faces:
- :class:`bpy.types.MeshPolygon` -
this is the data structure which now stores faces in object mode
- :class:`bpy.types.MeshPolygon` --
this is the data structure which now stores faces in Object-Mode
(access as ``mesh.polygons`` rather than ``mesh.faces``).
- :class:`bpy.types.MeshLoopTriangle` -
- :class:`bpy.types.MeshLoopTriangle` --
the result of tessellating polygons into triangles
(access as ``mesh.loop_triangles``).
- :class:`bmesh.types.BMFace` -
the polygons as used in editmode.
- :class:`bmesh.types.BMFace` --
the polygons as used in Edit-Mode.
For the purpose of the following documentation,
these will be referred to as polygons, loop triangles and bmesh-faces respectively.
these will be referred to as polygons, loop triangles and BMesh-faces respectively.
5+ sided faces will be referred to as ``ngons``.
Faces with five or more sides will be referred to as ``ngons``.
Support Overview
@ -216,58 +208,58 @@ Support Overview
- Unusable *(read-only)*.
- Best
* - Export/Output
- Good *(ngon support)*
- Good *(When ngons can't be used)*
- Good *(ngons, extra memory overhead)*
- Good *(n-gon support)*
- Good *(When n-gons cannot be used)*
- Good *(n-gons, extra memory overhead)*
.. note::
Using the :mod:`bmesh` API is completely separate API from :mod:`bpy`,
typically you would would use one or the other based on the level of editing needed,
typically you would use one or the other based on the level of editing needed,
not simply for a different way to access faces.
Creating
--------
All 3 datatypes can be used for face creation.
All three data types can be used for face creation:
- polygons are the most efficient way to create faces but the data structure is _very_ rigid and inflexible,
- Polygons are the most efficient way to create faces but the data structure is *very* rigid and inflexible,
you must have all your vertices and faces ready and create them all at once.
This is further complicated by the fact that each polygon does not store its own verts,
This is further complicated by the fact that each polygon does not store its own vertices,
rather they reference an index and size in :class:`bpy.types.Mesh.loops` which are a fixed array too.
- bmesh-faces are most likely the easiest way for new scripts to create faces,
since faces can be added one by one and the api has features intended for mesh manipulation.
- BMesh-faces are most likely the easiest way to create faces in new scripts,
since faces can be added one by one and the API has features intended for mesh manipulation.
While :class:`bmesh.types.BMesh` uses more memory it can be managed by only operating on one mesh at a time.
Editing
-------
Editing is where the 3 data types vary most.
Editing is where the three data types vary most.
- Polygons are very limited for editing,
changing materials and options like smooth works but for anything else
they are too inflexible and are only intended for storage.
- Tessfaces should not be used for editing geometry because doing so will cause existing ngons to be tessellated.
- BMesh-Faces are by far the best way to manipulate geometry.
- Tessfaces should not be used for editing geometry because doing so will cause existing n-gons to be tessellated.
- BMesh-faces are by far the best way to manipulate geometry.
Exporting
---------
All 3 data types can be used for exporting,
the choice mostly depends on whether the target format supports ngons or not.
All three data types can be used for exporting,
the choice mostly depends on whether the target format supports n-gons or not.
- Polygons are the most direct & efficient way to export providing they convert into the output format easily enough.
- Tessfaces work well for exporting to formats which don't support ngons,
- Polygons are the most direct and efficient way to export providing they convert into the output format easily enough.
- Tessfaces work well for exporting to formats which don't support n-gons,
in fact this is the only place where their use is encouraged.
- BMesh-Faces can work for exporting too but may not be necessary if polygons can be used
since using bmesh gives some overhead because its not the native storage format in object mode.
since using BMesh gives some overhead because its not the native storage format in Object-Mode.
EditBones, PoseBones, Bone... Bones
===================================
Edit Bones, Pose Bones, Bone... Bones
=====================================
Armature Bones in Blender have three distinct data structures that contain them.
If you are accessing the bones through one of them, you may not have access to the properties you really need.
@ -280,43 +272,41 @@ If you are accessing the bones through one of them, you may not have access to t
Edit Bones
----------
``bpy.context.object.data.edit_bones`` contains a editbones;
to access them you must set the armature mode to edit mode first (editbones do not exist in object or pose mode).
``bpy.context.object.data.edit_bones`` contains an edit bones;
to access them you must set the armature mode to Edit-Mode first (edit bones do not exist in Object or Pose-Mode).
Use these to create new bones, set their head/tail or roll, change their parenting relationships to other bones, etc.
Example using :class:`bpy.types.EditBone` in armature editmode:
This is only possible in edit mode.
Example using :class:`bpy.types.EditBone` in armature Edit-Mode
which is only possible in Edit-Mode:
>>> bpy.context.object.data.edit_bones["Bone"].head = Vector((1.0, 2.0, 3.0))
This will be empty outside of editmode.
This will be empty outside of Edit-Mode:
>>> mybones = bpy.context.selected_editable_bones
Returns an editbone only in edit mode.
Returns an edit bone only in Edit-Mode:
>>> bpy.context.active_bone
Bones (Object Mode)
Bones (Object-Mode)
-------------------
``bpy.context.object.data.bones`` contains bones.
These *live* in object mode, and have various properties you can change,
These *live* in Object-Mode, and have various properties you can change,
note that the head and tail properties are read-only.
Example using :class:`bpy.types.Bone` in object or pose mode:
Returns a bone (not an editbone) outside of edit mode
Example using :class:`bpy.types.Bone` in Object or Pose-Mode
returning a bone (not an edit bone) outside of Edit-Mode:
>>> bpy.context.active_bone
This works, as with blender the setting can be edited in any mode
This works, as with Blender the setting can be edited in any mode:
>>> bpy.context.object.data.bones["Bone"].use_deform = True
Accessible but read-only
Accessible but read-only:
>>> tail = myobj.data.bones["Bone"].tail
@ -326,42 +316,42 @@ Pose Bones
``bpy.context.object.pose.bones`` contains pose bones.
This is where animation data resides, i.e. animatable transformations
are applied to pose bones, as are constraints and ik-settings.
are applied to pose bones, as are constraints and IK-settings.
Examples using :class:`bpy.types.PoseBone` in object or pose mode:
Examples using :class:`bpy.types.PoseBone` in Object or Pose-Mode:
.. code-block:: python
# Gets the name of the first constraint (if it exists)
bpy.context.object.pose.bones["Bone"].constraints[0].name
# Gets the last selected pose bone (pose mode only)
# Gets the last selected pose bone (Pose-Mode only)
bpy.context.active_pose_bone
.. note::
Notice the pose is accessed from the object rather than the object data,
this is why blender can have 2 or more objects sharing the same armature in different poses.
this is why Blender can have two or more objects sharing the same armature in different poses.
.. note::
Strictly speaking PoseBone's are not bones, they are just the state of the armature,
Strictly speaking pose bones are not bones, they are just the state of the armature,
stored in the :class:`bpy.types.Object` rather than the :class:`bpy.types.Armature`,
the real bones are however accessible from the pose bones - :class:`bpy.types.PoseBone.bone`
yet the real bones are accessible from the pose bones via :class:`bpy.types.PoseBone.bone`.
Armature Mode Switching
-----------------------
While writing scripts that deal with armatures you may find you have to switch between modes,
when doing so take care when switching out of edit-mode not to keep references
to the edit-bones or their head/tail vectors.
Further access to these will crash blender so its important the script
when doing so take care when switching out of Edit-Mode not to keep references
to the edit bones or their head/tail vectors.
Further access to these will crash Blender so its important the script
clearly separates sections of the code which operate in different modes.
This is mainly an issue with editmode since pose data can be manipulated without having to be in pose mode,
however for operator access you may still need to enter pose mode.
This is mainly an issue with Edit-Mode since pose data can be manipulated without having to be in Pose-Mode,
yet for operator access you may still need to enter Pose-Mode.
Data Names
@ -372,8 +362,7 @@ Naming Limitations
------------------
A common mistake is to assume newly created data is given the requested name.
This can cause bugs when you add some data (normally imported) then reference it later by name.
This can cause bugs when you add data (normally imported) then reference it later by name:
.. code-block:: python
@ -383,7 +372,7 @@ This can cause bugs when you add some data (normally imported) then reference it
bpy.data.meshes[meshid]
Or with name assignment...
Or with name assignment:
.. code-block:: python
@ -397,12 +386,12 @@ Data names may not match the assigned values if they exceed the maximum length,
Its better practice not to reference objects by names at all,
once created you can store the data in a list, dictionary, on a class etc,
once created you can store the data in a list, dictionary, on a class, etc;
there is rarely a reason to have to keep searching for the same data by name.
If you do need to use name references, its best to use a dictionary to maintain
a mapping between the names of the imported assets and the newly created data,
this way you don't run this risk of referencing existing data from the blend file, or worse modifying it.
this way you don't run this risk of referencing existing data from the blend-file, or worse modifying it.
.. code-block:: python
@ -421,17 +410,14 @@ this way you don't run this risk of referencing existing data from the blend fil
Library Collisions
------------------
Blender keeps data names unique - :class:`bpy.types.ID.name` so you can't name two objects,
meshes, scenes etc the same thing by accident.
However when linking in library data from another blend file naming collisions can occur,
Blender keeps data names unique (:class:`bpy.types.ID.name`) so you can't name two objects,
meshes, scenes, etc., the same by accident.
However, when linking in library data from another blend-file naming collisions can occur,
so its best to avoid referencing data by name at all.
This can be tricky at times and not even blender handles this correctly in some case
(when selecting the modifier object for eg you can't select between multiple objects with the same name),
but its still good to try avoid problems in this area.
This can be tricky at times and not even Blender handles this correctly in some case
(when selecting the modifier object for e.g. you can't select between multiple objects with the same name),
but its still good to try avoiding these problems in this area.
If you need to select between local and library data, there is a feature in ``bpy.data`` members to allow for this.
.. code-block:: python
@ -454,18 +440,17 @@ If you need to select between local and library data, there is a feature in ``bp
Relative File Paths
===================
Blenders relative file paths are not compatible with standard Python modules such as ``sys`` and ``os``.
Blender's relative file paths are not compatible with standard Python modules such as ``sys`` and ``os``.
Built-in Python functions don't understand Blender's ``//`` prefix which denotes the blend-file path.
Built in Python functions don't understand blenders ``//`` prefix which denotes the blend file path.
A common case where you would run into this problem is when exporting a material with associated image paths.
A common case where you would run into this problem is when exporting a material with associated image paths:
>>> bpy.path.abspath(image.filepath)
When using blender data from linked libraries there is an unfortunate complication
since the path will be relative to the library rather than the open blend file.
When the data block may be from an external blend file pass the library argument from the :class:`bpy.types.ID`.
When using Blender data from linked libraries there is an unfortunate complication
since the path will be relative to the library rather than the open blend-file.
When the data block may be from an external blend-file pass the library argument from the :class:`bpy.types.ID`.
>>> bpy.path.abspath(image.filepath, library=image.library)
@ -478,19 +463,15 @@ Unicode Problems
Python supports many different encodings so there is nothing stopping you from
writing a script in ``latin1`` or ``iso-8859-15``.
See `PEP 263 <https://www.python.org/dev/peps/pep-0263/>`__.
See `pep-0263 <https://www.python.org/dev/peps/pep-0263/>`_
However this complicates matters for Blender's Python API because ``.blend`` files don't have an explicit encoding.
To avoid the problem for Python integration and script authors we have decided all strings in blend files
However, this complicates matters for Blender's Python API because ``.blend`` files don't have an explicit encoding.
To avoid the problem for Python integration and script authors we have decided all strings in blend-files
**must** be ``UTF-8``, ``ASCII`` compatible.
This means assigning strings with different encodings to an object names for instance will raise an error.
Paths are an exception to this rule since we cannot ignore the existence of non ``UTF-8`` paths on users file-system.
This means seemingly harmless expressions can raise errors, eg.
Paths are an exception to this rule since the existence of non-UTF-8 paths on user's file system cannot be ignored.
This means seemingly harmless expressions can raise errors, e.g:
>>> print(bpy.data.filepath)
UnicodeEncodeError: 'ascii' codec can't encode characters in position 10-21: ordinal not in range(128)
@ -501,7 +482,7 @@ This means seemingly harmless expressions can raise errors, eg.
TypeError: bpy_struct: item.attr= val: Object.name expected a string type, not str
Here are 2 ways around filesystem encoding issues:
Here are two ways around file-system encoding issues:
>>> print(repr(bpy.data.filepath))
@ -512,11 +493,11 @@ Here are 2 ways around filesystem encoding issues:
Unicode encoding/decoding is a big topic with comprehensive Python documentation,
to avoid getting stuck too deep in encoding problems - here are some suggestions:
to keep it short about encoding problems -- here are some suggestions:
- Always use utf-8 encoding or convert to utf-8 where the input is unknown.
- Avoid manipulating filepaths as strings directly, use ``os.path`` functions instead.
- Use ``os.fsencode()`` / ``os.fsdecode()`` instead of built in string decoding functions when operating on paths.
- Always use UTF-8 encoding or convert to UTF-8 where the input is unknown.
- Avoid manipulating file paths as strings directly, use ``os.path`` functions instead.
- Use ``os.fsencode()`` or ``os.fsdecode()`` instead of built-in string decoding functions when operating on paths.
- To print paths or to include them in the user interface use ``repr(path)`` first
or ``"%r" % path`` with string formatting.
@ -528,11 +509,11 @@ to avoid getting stuck too deep in encoding problems - here are some suggestions
some importers do this.
Strange errors using 'threading' module
=======================================
Strange Errors when Using the 'Threading' Module
================================================
Python threading with Blender only works properly when the threads finish up before the script does.
By using ``threading.join()`` for example.
Python threading with Blender only works properly when the threads finish up before the script does,
for example by using ``threading.join()``.
Here is an example of threading supported by Blender:
@ -571,8 +552,8 @@ Here is an example of threading supported by Blender:
t.join()
This an example of a timer which runs many times a second and moves
the default cube continuously while Blender runs **(Unsupported)**.
This an example of a timer which runs many times a second
and moves the default cube continuously while Blender runs **(Unsupported)**.
.. code-block:: python
@ -592,33 +573,33 @@ the default cube continuously while Blender runs **(Unsupported)**.
Use cases like the one above which leave the thread running once the script finishes
may seem to work for a while but end up causing random crashes or errors in Blender's own drawing code.
So far, no work has gone into making Blender's Python integration thread safe,
so until its properly supported, best not make use of this.
So far, no work has been done to make Blender's Python integration thread safe,
so until it's properly supported, it's best not make use of this.
.. note::
Pythons threads only allow co-currency and won't speed up your scripts on multi-processor systems,
the ``subprocess`` and ``multiprocess`` modules can be used with Blender and make use of multiple CPU's too.
Python threads only allow concurrency and won't speed up your scripts on multiprocessor systems,
the ``subprocess`` and ``multiprocess`` modules can be used with Blender to make use of multiple CPUs too.
Help! My script crashes Blender
===============================
**TL;DR:** Do not keep direct references to Blender data (of any kind) when modifying the container
of that data, and/or when some undo/redo may happen (e.g. during modal operators execution...).
:abbr:`TL;DR (Too long; didn't read.)` Do not keep direct references to Blender data (of any kind)
when modifying the container of that data, and/or when some undo/redo may happen
(e.g. during modal operators execution...).
Instead, use indices (or other data always stored by value in Python, like string keys...),
that allow you to get access to the desired data.
Ideally it would be impossible to crash Blender from Python
however there are some problems with the API where it can be made to crash.
Ideally it would be impossible to crash Blender from Python,
however, there are some problems with the API where it can be made to crash.
Strictly speaking this is a bug in the API but fixing it would mean adding memory verification
on every access since most crashes are caused by the Python objects referencing Blenders memory directly,
on every access since most crashes are caused by the Python objects referencing Blender's memory directly,
whenever the memory is freed or re-allocated, further Python access to it can crash the script.
But fixing this would make the scripts run very slow,
or writing a very different kind of API which doesn't reference the memory directly.
Here are some general hints to avoid running into these problems.
Here are some general hints to avoid running into these problems:
- Be aware of memory limits,
especially when working with large lists since Blender can crash simply by running out of memory.
@ -631,16 +612,16 @@ Here are some general hints to avoid running into these problems.
- Modules or classes that remain active while Blender is used,
should not hold references to data the user may remove, instead,
fetch data from the context each time the script is activated.
- Crashes may not happen every time, they may happen more on some configurations/operating-systems.
- Be wary of recursive patterns, those are very efficient at hiding the issues described here.
- See last sub-section about `Unfortunate Corner Cases`_ for some known breaking exceptions.
- Crashes may not happen every time, they may happen more on some configurations or operating systems.
- Be careful with recursive patterns, those are very efficient at hiding the issues described here.
- See last subsection about `Unfortunate Corner Cases`_ for some known breaking exceptions.
.. note::
To find the line of your script that crashes you can use the ``faulthandler`` module.
See the `faulthandler docs <https://docs.python.org/dev/library/faulthandler.html>`_.
See the `Faulthandler docs <https://docs.python.org/dev/library/faulthandler.html>`__.
While the crash may be in Blenders C/C++ code,
While the crash may be in Blender's C/C++ code,
this can help a lot to track down the area of the script that causes the crash.
.. note::
@ -654,7 +635,7 @@ Here are some general hints to avoid running into these problems.
in any possible way.
**Don’t:**
.. rubric:: Do not:
.. code-block:: python
@ -673,7 +654,7 @@ Here are some general hints to avoid running into these problems.
first_item.name = "foobar"
**Do:**
.. rubric:: Do:
.. code-block:: python
@ -696,33 +677,31 @@ Here are some general hints to avoid running into these problems.
Undo/Redo
---------
Undo invalidates all :class:`bpy.types.ID` instances (Object, Scene, Mesh, Lamp... etc).
Undo invalidates all :class:`bpy.types.ID` instances (Object, Scene, Mesh, Light, etc.).
This example shows how you can tell undo changes the memory locations.
This example shows how you can tell undo changes the memory locations:
>>> hash(bpy.context.object)
-9223372036849950810
>>> hash(bpy.context.object)
-9223372036849950810
# ... move the active object, then undo
Move the active object, then undo:
>>> hash(bpy.context.object)
-9223372036849951740
As suggested above, simply not holding references to data when Blender is used
interactively by the user is the only way to ensure the script doesn't become unstable.
interactively by the user is the only way to make sure that the script doesn't become unstable.
Undo & Library Data
^^^^^^^^^^^^^^^^^^^
One of the advantages with Blenders library linking system that undo
One of the advantages with Blender's library linking system that undo
can skip checking changes in library data since it is assumed to be static.
Tools in Blender are not allowed to modify library data.
Python however does not enforce this restriction.
But Python does not enforce this restriction.
This can be useful in some cases, using a script to adjust material values for example.
But its also possible to use a script to make library data point to newly created local data,
@ -733,13 +712,13 @@ So it's best to consider modifying library data an advanced usage of the API
and only to use it when you know what you're doing.
Edit Mode / Memory Access
Edit-Mode / Memory Access
-------------------------
Switching edit-mode ``bpy.ops.object.mode_set(mode='EDIT')`` / ``bpy.ops.object.mode_set(mode='OBJECT')``
Switching mode ``bpy.ops.object.mode_set(mode='EDIT')`` or ``bpy.ops.object.mode_set(mode='OBJECT')``
will re-allocate objects data,
any references to a meshes vertices/polygons/uvs, armatures bones,
curves points etc cannot be accessed after switching edit-mode.
any references to a meshes vertices/polygons/UVs, armatures bones,
curves points, etc. cannot be accessed after switching mode.
Only the reference to the data its self can be re-accessed, the following example will crash.
@ -754,7 +733,7 @@ Only the reference to the data its self can be re-accessed, the following exampl
print(polygons)
So after switching edit-mode you need to re-access any object data variables,
So after switching mode you need to re-access any object data variables,
the following example shows how to avoid the crash above.
.. code-block:: python
@ -770,7 +749,7 @@ the following example shows how to avoid the crash above.
These kinds of problems can happen for any functions which re-allocate
the object data but are most common when switching edit-mode.
the object data but are most common when switching mode.
Array Re-Allocation
@ -791,21 +770,20 @@ internally the array which stores this data is re-allocated.
This can be avoided by re-assigning the point variables after adding the new one or by storing
indices to the points rather than the points themselves.
The best way is to sidestep the problem altogether add all the points to the curve at once.
This means you don't have to worry about array re-allocation and its faster too
since reallocating the entire array for every point added is inefficient.
The best way is to sidestep the problem altogether by adding all the points to the curve at once.
This means you don't have to worry about array re-allocation and it's faster too
since re-allocating the entire array for every added point is inefficient.
Removing Data
-------------
**Any** data that you remove shouldn't be modified or accessed afterwards,
this includes f-curves, drivers, render layers, timeline markers, modifiers, constraints
along with objects, scenes, collections, bones.. etc.
this includes: F-curves, drivers, render layers, timeline markers, modifiers, constraints
along with objects, scenes, collections, bones, etc.
The ``remove()`` api calls will invalidate the data they free to prevent common mistakes.
The following example shows how this precaution works.
The ``remove()`` API calls will invalidate the data they free to prevent common mistakes.
The following example shows how this precaution works:
.. code-block:: python
@ -818,7 +796,7 @@ The following example shows how this precaution works.
But take care because this is limited to scripts accessing the variable which is removed,
the next example will still crash.
the next example will still crash:
.. code-block:: python
@ -835,8 +813,8 @@ Besides all expected cases listed above, there are a few others that should not
an issue but, due to internal implementation details, currently are:
- ``Object.hide_viewport``, ``Object.hide_select`` and ``Object.hide_render``:
Setting any of those booleans will trigger a rebuild of Collection caches, hence breaking
any current iteration over ``Collection.all_objects``.
Setting any of those Booleans will trigger a rebuild of Collection caches,
thus breaking any current iteration over ``Collection.all_objects``.
sys.exit
@ -848,5 +826,5 @@ as if Blender is crashing since ``sys.exit()`` will close Blender immediately.
For example, the ``argparse`` module will print an error and exit if the arguments are invalid.
An ugly way of troubleshooting this is to set ``sys.exit = None`` and see what line of Python code is quitting,
An dirty way of troubleshooting this is to set ``sys.exit = None`` and see what line of Python code is quitting,
you could of course replace ``sys.exit`` with your own function but manipulating Python in this way is bad practice.

118
doc/python_api/rst/info_overview.rst
View File

@ -1,4 +1,3 @@
.. _info_overview:
*******************
@ -6,24 +5,24 @@ Python API Overview
*******************
The purpose of this document is to explain how Python and Blender fit together,
covering some of the functionality that may not be obvious from reading the API
references and example scripts.
covering some of the functionality that may not be obvious from reading the API references
and example scripts.
Python in Blender
=================
Blender has an embedded Python interpreter which is loaded when Blender is started and stays
active while Blender is running. This interpreter runs scripts to draw the user interface
and is used for some of Blender’s internal tools as well.
Blender has an embedded Python interpreter which is loaded when Blender is started
and stays active while Blender is running. This interpreter runs scripts to draw the user interface
and is used for some of Blender's internal tools as well.
Blender's embedded interpreter provides a typical Python environment, so code from tutorials
on how to write Python scripts can also be run with Blender’s interpreter. Blender provides its
on how to write Python scripts can also be run with Blender's interpreter. Blender provides its
Python modules, such as :mod:`bpy` and :mod:`mathutils`, to the embedded interpreter so they can
be imported into a script and give access to Blender's data, classes, and functions. Scripts that
deal with Blender data will need to import the modules to work.
be imported into a script and give access to Blender's data, classes, and functions.
Scripts that deal with Blender data will need to import the modules to work.
Here is a simple example which moves a vertex attached to an object named **Cube**:
Here is a simple example which moves a vertex attached to an object named "Cube":
.. code-block:: python
@ -31,7 +30,7 @@ Here is a simple example which moves a vertex attached to an object named **Cube
bpy.data.objects["Cube"].data.vertices[0].co.x += 1.0
This modifies Blender's internal data directly.
When you run this in the interactive console you will see the 3D viewport update.
When you run this in the interactive console you will see the 3D Viewport update.
The Default Environment
@ -41,7 +40,7 @@ When developing your own scripts it may help to understand how Blender sets up i
Many Python scripts come bundled with Blender and can be used as a reference
because they use the same API that script authors write tools in.
Typical usage for scripts include: user interface, import/export,
scene manipulation, automation, defining your own toolset and customization.
scene manipulation, automation, defining your own tool set and customization.
On startup Blender scans the ``scripts/startup/`` directory for Python modules and imports them.
The exact location of this directory depends on your installation.
@ -54,8 +53,8 @@ Script Loading
This may seem obvious, but it is important to note the difference between
executing a script directly and importing a script as a module.
Extending Blender by executing a script directly means the classes that the script
defines remain available inside Blender after the script finishes execution.
Extending Blender by executing a script directly means the classes that the script defines
remain available inside Blender after the script finishes execution.
Using scripts this way makes future access to their classes
(to unregister them for example) more difficult compared to importing the scripts as modules.
When a script is imported as a module, its class instances will remain
@ -63,12 +62,11 @@ inside the module and can be accessed later on by importing that module again.
For this reason it is preferable to avoid directly executing scripts that extend Blender by registering classes.
Here are some ways to run scripts directly in Blender:
Here are some ways to run scripts directly in Blender.
- Loaded in the text editor and press **Run Script**.
- Loaded in the text editor and press *Run Script*.
- Typed or pasted into the interactive console.
- Execute a Python file from the command line with Blender, eg:
- Execute a Python file from the command line with Blender, e.g:
.. code-block:: sh
@ -77,24 +75,22 @@ Here are some ways to run scripts directly in Blender.
To run as modules:
- The obvious way, ``import some_module`` command from the text window or interactive console.
- Open as a text block and tick "Register" option, this will load with the blend file.
- copy into one of the directories ``scripts/startup``, where they will be automatically imported on startup.
- define as an add-on, enabling the add-on will load it as a Python module.
- The obvious way, ``import some_module`` command from the text editor or interactive console.
- Open as a text data-block and check the *Register* option, this will load with the blend-file.
- Copy into one of the directories ``scripts/startup``, where they will be automatically imported on startup.
- Define as an add-on, enabling the add-on will load it as a Python module.
Add-ons
-------
Some of Blenders functionality is best kept optional,
alongside scripts loaded at startup we have add-ons which are kept in their own directory ``scripts/addons``,
and only load on startup if selected from the user preferences.
The only difference between add-ons and built-in Python modules is that add-ons must contain a ``bl_info``
variable which Blender uses to read metadata such as name, author, category and URL.
The User Preferences add-on listing uses **bl_info** to display information about each add-on.
Some of Blender's functionality is best kept optional,
alongside scripts loaded at startup there are add-ons which are kept in their own directory ``scripts/addons``,
They are only loaded on startup if selected from the user preferences.
The only difference between add-ons and built-in Python modules is that add-ons must contain a ``bl_info`` variable
which Blender uses to read metadata such as name, author, category and project link.
The User Preferences add-on listing uses ``bl_info`` to display information about each add-on.
`See Add-ons <https://wiki.blender.org/index.php/Dev:Py/Scripts/Guidelines/Addons>`__
for details on the ``bl_info`` dictionary.
@ -105,7 +101,7 @@ Integration through Classes
Running Python scripts in the text editor is useful for testing but you'll
want to extend Blender to make tools accessible like other built-in functionality.
The Blender Python api allows integration for:
The Blender Python API allows integration for:
- :class:`bpy.types.Panel`
- :class:`bpy.types.Menu`
@ -114,13 +110,12 @@ The Blender Python api allows integration for:
- :class:`bpy.types.KeyingSet`
- :class:`bpy.types.RenderEngine`
This is intentionally limited. Currently, for more advanced features such as mesh modifiers,
object types, or shader nodes, C/C++ must be used.
For Python integration Blender defines methods which are common to all types.
This works by creating a Python subclass of a Blender class which contains variables and functions
specified by the parent class which are pre-defined to interface with Blender.
specified by the parent class which are predefined to interface with Blender.
For example:
@ -137,22 +132,20 @@ For example:
bpy.utils.register_class(SimpleOperator)
First note that we subclass a member of :mod:`bpy.types`,
First note that it defines a subclass as a member of :mod:`bpy.types`,
this is common for all classes which can be integrated with Blender and
used so we know if this is an Operator and not a Panel when registering.
is used to distinguish an Operator from a Panel when registering.
Both class properties start with a ``bl_`` prefix.
This is a convention used to distinguish Blender properties from those you add yourself.
Next see the execute function, which takes an instance of the operator and the current context.
A common prefix is not used for functions.
Lastly the register function is called, this takes the class and loads it into Blender. See `Class Registration`_.
Regarding inheritance, Blender doesn't impose restrictions on the kinds of class inheritance used,
the registration checks will use attributes and functions defined in parent classes.
class mix-in example:
Class mix-in example:
.. code-block:: python
@ -173,8 +166,8 @@ While ``__init__()`` and ``__del__()`` will be called if defined,
the class instances lifetime only spans the execution.
So a panel for example will have a new instance for every redraw,
for this reason there is rarely a cause to store variables in the panel instance.
Instead, persistent variables should be stored in Blenders
ata so that the state can be restored when Blender is restarted.
Instead, persistent variables should be stored in Blender's data
so that the state can be restored when Blender is restarted.
.. note::
@ -182,15 +175,14 @@ ata so that the state can be restored when Blender is restarted.
So once the class is registered with Blender, instancing the class and calling the functions is left up to Blender.
In fact you cannot instance these classes from the script as you would expect with most Python API's.
To run operators you can call them through the operator api, eg:
To run operators you can call them through the operator API, e.g:
.. code-block:: python
import bpy
bpy.ops.object.simple_operator()
User interface classes are given a context in which to draw, buttons window, file header, toolbar etc,
User interface classes are given a context in which to draw, buttons, window, file header, toolbar, etc.,
then they are drawn when that area is displayed so they are never called by Python scripts directly.
@ -205,7 +197,7 @@ Module Registration
Blender modules loaded at startup require ``register()`` and ``unregister()`` functions.
These are the *only* functions that Blender calls from your code, which is otherwise a regular Python module.
A simple Blender/Python module can look like this:
A simple Blender Python module can look like this:
.. code-block:: python
@ -225,16 +217,15 @@ A simple Blender/Python module can look like this:
These functions usually appear at the bottom of the script containing class registration sometimes adding menu items.
You can also use them for internal purposes setting up data for your own tools but take care
since register won't re-run when a new blend file is loaded.
since register won't re-run when a new blend-file is loaded.
The register/unregister calls are used so it's possible to toggle add-ons and reload scripts while Blender runs.
If the register calls were placed in the body of the script, registration would be called on import,
meaning there would be no distinction between importing a module or loading its classes into Blender.
This becomes problematic when a script imports classes from another module
making it difficult to manage which classes are being loaded and when.
The last 2 lines are only for testing:
The last two lines are only for testing:
.. code-block:: python
@ -251,7 +242,6 @@ Class Registration
Registering a class with Blender results in the class definition being loaded into Blender,
where it becomes available alongside existing functionality.
Once this class is loaded you can access it from :mod:`bpy.types`,
using the ``bl_idname`` rather than the classes original name.
@ -271,23 +261,23 @@ Using the function arguments ``def execute(self, context, spam)``, will raise an
``ValueError: expected Operator, SimpleOperator class "execute" function to have 2 args, found 3``
Using ``bl_idname = 1`` will raise.
Using ``bl_idname = 1`` will raise:
``TypeError: validating class error: Operator.bl_idname expected a string type, not int``
Inter Classes Dependencies
^^^^^^^^^^^^^^^^^^^^^^^^^^
Inter-Class Dependencies
^^^^^^^^^^^^^^^^^^^^^^^^
When customizing Blender you may want to group your own settings together,
after all, they will likely have to co-exist with other scripts.
To group these properties classes need to be defined,
for groups within groups or collections within groups
you can find yourself having to deal with order of registration/unregistration.
you can't avoid having to deal with the order of registration/unregistration.
Custom properties groups are themselves classes which need to be registered.
Say you want to store material settings for a custom engine.
For example, if you want to store material settings for a custom engine:
.. code-block:: python
@ -311,7 +301,7 @@ Say you want to store material settings for a custom engine.
.. note::
*The class must be registered before being used in a property, failing to do so will raise an error:*
The class **must be** registered before being used in a property, failing to do so will raise an error:
``ValueError: bpy_struct "Material" registration error: my_custom_props could not register``
@ -341,17 +331,17 @@ Say you want to store material settings for a custom engine.
if __name__ == "__main__":
register()
.. note::
.. important::
*The lower most class needs to be registered first and that unregister() is a mirror of register()*
The lower most class needs to be registered first and that ``unregister()`` is a mirror of ``register()``.
Manipulating Classes
^^^^^^^^^^^^^^^^^^^^
Properties can be added and removed as Blender runs,
normally happens on register or unregister but for some
special cases it may be useful to modify types as the script runs.
normally done on register or unregister but for some special cases
it may be useful to modify types as the script runs.
For example:
@ -362,7 +352,7 @@ For example:
# remove
del bpy.types.Object.my_float
This works just as well for PropertyGroup subclasses you define yourself.
This works just as well for ``PropertyGroup`` subclasses you define yourself.
.. code-block:: python
@ -370,7 +360,7 @@ This works just as well for PropertyGroup subclasses you define yourself.
pass
MyPropGroup.my_float: bpy.props.FloatProperty()
...this is equivalent to:
This is equivalent to:
.. code-block:: python
@ -378,11 +368,11 @@ This works just as well for PropertyGroup subclasses you define yourself.
my_float: bpy.props.FloatProperty()
Dynamic Defined-Classes (Advanced)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Dynamic Class Definition (Advanced)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
In some cases the specifier for data may not be in Blender, renderman shader definitions
for example, and it may be useful to define them as types and remove them on the fly.
In some cases the specifier for data may not be in Blender, for example a external render engines shader definitions,
and it may be useful to define them as types and remove them on the fly.
.. code-block:: python

198
doc/python_api/rst/info_quickstart.rst
View File

@ -1,19 +1,16 @@
.. _info_quickstart:
***********************
Quickstart Introduction
***********************
**********
Quickstart
**********
Preface
=======
This :abbr:`API (Application Programming Interface)` is generally stable
but some areas are still being extended and improved.
This API is generally stable but some areas are still being added and improved.
The Blender/Python API can do the following:
.. rubric:: Blender Python API features:
- Edit any data the user interface can (Scenes, Meshes, Particles etc.).
- Modify user preferences, key-maps and themes.
- Modify user preferences, keymaps and themes.
- Run tools with own settings.
- Create user interface elements such as menus, headers and panels.
- Create new tools.
@ -21,10 +18,10 @@ The Blender/Python API can do the following:
- Create new rendering engines that integrate with Blender.
- Subscribe to changes to data and it's properties.
- Define new settings in existing Blender data.
- Draw in the 3D view using Python.
- Draw in the 3D Viewport using Python.
The Blender/Python API **can't** (yet)...
.. rubric:: (Still) missing features:
- Create new space types.
- Assign custom properties to every type.
@ -33,22 +30,21 @@ The Blender/Python API **can't** (yet)...
Before Starting
===============
This document isn't intended to fully cover each topic.
Rather, its purpose is to familiarize you with Blender Python API.
This document its intended to familiarize you with Blender Python API
but not to fully cover each topic.
A quick list of helpful things to know before starting:
- Blender uses Python 3.x; some online documentation still assumes 2.x.
- Blender uses Python 3.x; some online documentation still assumes version 2.x.
- The interactive console is great for testing one-liners.
It also has autocompletion so you can inspect the API quickly.
- Button tool tips show Python attributes and operator names.
- Right clicking on buttons and menu items directly links to API documentation.
- For more examples, the text menu has a templates section where some example operators can be found.
- Button tooltips show Python attributes and operator names.
- The context menu of buttons directly links to this API documentation.
- More operator examples can be found in the text editor's template menu.
- To examine further scripts distributed with Blender, see:
| ``scripts/startup/bl_ui`` for the user interface,
| ``scripts/startup/bl_operators`` for operators.
- ``scripts/startup/bl_ui`` for the user interface.
- ``scripts/startup/bl_operators`` for operators.
Exact location depends on platform, see:
:ref:`directory layout docs <blender_manual:blender-directory-layout>`.
@ -59,19 +55,14 @@ Running Scripts
The two most common ways to execute Python scripts are using the built-in
text editor or entering commands in the Python console.
Both the *Text Editor* and *Python Console* are space types you can select from the view header.
Both the *Text Editor* and *Python Console* are space types you can select from the header.
Rather than manually configuring your spaces for Python development,
you may prefer to use the *Scripting* screen, included default with Blender,
accessible from the top headers screen selector.
you can use the *Scripting* workspace accessible from the Topbar tabs.
From the text editor you can open ``.py`` files or paste then from the clipboard, then test using *Run Script*.
The Python Console is typically used for typing in snippets and for testing to get immediate feedback,
but can also have entire scripts pasted into it.
Scripts can also run from the command line with Blender but to learn Blender/Python this isn't essential.
Scripts can also run from the command line with Blender but to learn scripting in Blender this isn't essential.
Key Concepts
@ -80,14 +71,13 @@ Key Concepts
Data Access
-----------
Accessing DataBlocks
^^^^^^^^^^^^^^^^^^^^
Accessing Data-Blocks
^^^^^^^^^^^^^^^^^^^^^
Python accesses Blender's data in the same way as the animation system and user interface;
this implies that any setting that can be changed via a button can also be changed from Python.
Accessing data from the currently loaded blend file is done with the module :mod:`bpy.data`.
This gives access to library data. For example:
You can access Blender's data with the Python API in the same way as the animation system or user interface;
this implies that any setting that can be changed via a button can also be changed with Python.
Accessing data from the currently loaded blend-file is done with the module :mod:`bpy.data`.
It gives access to library data, for example:
>>> bpy.data.objects
<bpy_collection[3], BlendDataObjects>
@ -99,12 +89,11 @@ This gives access to library data. For example:
<bpy_collection[1], BlendDataMaterials>
About Collections
^^^^^^^^^^^^^^^^^
Accessing Collections
^^^^^^^^^^^^^^^^^^^^^
You'll notice that an index as well as a string can be used to access members of the collection.
Unlike Python's dictionaries, both methods are acceptable;
You will notice that an index as well as a string can be used to access members of the collection.
Unlike Python dictionaries, both methods are available;
however, the index of a member may change while running Blender.
>>> list(bpy.data.objects)
@ -120,7 +109,7 @@ however, the index of a member may change while running Blender.
Accessing Attributes
^^^^^^^^^^^^^^^^^^^^
Once you have a data block, such as a material, object, collections etc.,
Once you have a data-block, such as a material, object, collection, etc.,
its attributes can be accessed much like you would change a setting using the graphical interface.
In fact, the tooltip for each button also displays the Python attribute
which can help in finding what settings to change in a script.
@ -135,8 +124,8 @@ which can help in finding what settings to change in a script.
bpy.data.materials['MyMaterial']
For testing what data to access it's useful to use the "Console", which is its own space type.
This supports auto-complete, giving you a fast way to dig into different data in your file.
For testing what data to access it's useful to use the Python Console, which is its own space type.
This supports auto-complete, giving you a fast way to explore the data in your file.
Example of a data path that can be quickly found via the console:
@ -149,8 +138,8 @@ Example of a data path that can be quickly found via the console:
Data Creation/Removal
^^^^^^^^^^^^^^^^^^^^^
Those of you familiar with other Python API's may be surprised that
new data-blocks in the bpy API can't be created by calling the class:
When you are familiar with other Python APIs you may be surprised that
new data-blocks in the bpy API cannot be created by calling the class:
>>> bpy.types.Mesh()
Traceback (most recent call last):
@ -159,10 +148,10 @@ new data-blocks in the bpy API can't be created by calling the class:
This is an intentional part of the API design.
The Blender/Python API can't create Blender data that exists outside the main Blender database
(accessed through :mod:`bpy.data`), because this data is managed by Blender (save/load/undo/append... etc).
The Blender Python API can't create Blender data that exists outside the main Blender database
(accessed through :mod:`bpy.data`), because this data is managed by Blender (save, load, undo, append, etc).
Data is added and removed via methods on the collections in :mod:`bpy.data`, eg:
Data is added and removed via methods on the collections in :mod:`bpy.data`, e.g:
>>> mesh = bpy.data.meshes.new(name="MyMesh")
>>> print(mesh)
@ -174,14 +163,12 @@ Data is added and removed via methods on the collections in :mod:`bpy.data`, eg:
Custom Properties
^^^^^^^^^^^^^^^^^
Python can access properties on any datablock that has an ID
(data that can be linked in and accessed from :mod:`bpy.data`.
When assigning a property, you can make up your own names,
these will be created when needed or overwritten if they exist.
Python can access properties on any data-block that has an ID
(data that can be linked in and accessed from :mod:`bpy.data`).
When assigning a property, you can pick your own names,
these will be created when needed or overwritten if they already exist.
This data is saved with the blend file and copied with objects.
Example:
This data is saved with the blend-file and copied with objects, for example:
.. code-block:: python
@ -201,10 +188,10 @@ Example:
del collection["MySettings"]
Note that these properties can only be assigned basic Python types.
Note that these properties can only be assigned basic Python types:
- int, float, string
- array of ints/floats
- array of ints or floats
- dictionary (only string keys are supported, values must be basic types too)
These properties are valid outside of Python. They can be animated by curves or used in driver paths.
@ -218,18 +205,16 @@ it's more common to operate on the user's selection.
The context is always available from ``bpy.context`` and can be used to get the active object, scene,
tool settings along with many other attributes.
Common-use cases:
Some common use cases are:
>>> bpy.context.object
>>> bpy.context.selected_objects
>>> bpy.context.visible_bones
Note that the context is read-only.
These values cannot be modified directly,
though they may be changed by running API functions or by using the data API.
Note that the context is read-only, which means that these values cannot be modified directly.
But they can be changed by running API functions or by using the data API.
So ``bpy.context.active_object = obj`` will raise an error.
But ``bpy.context.view_layer.objects.active = obj`` works as expected.
The context attributes change depending on where they are accessed.
@ -257,7 +242,7 @@ Examples:
.. tip::
The :ref:`Operator Cheat Sheet <blender_manual:bpy.ops.wm.operator_cheat_sheet>`.
The :ref:`Operator Cheat Sheet <blender_manual:bpy.ops.wm.operator_cheat_sheet>`
gives a list of all operators and their default values in Python syntax, along with the generated docs.
This is a good way to get an overview of all Blender's operators.
@ -265,8 +250,8 @@ Examples:
Operator Poll()
^^^^^^^^^^^^^^^
Many operators have a "poll" function which may check that the cursor
is in a valid area or that the object is in the correct mode (Edit Mode, Weight Paint etc).
Many operators have a "poll" function which checks if the cursor
is in a valid area or if the object is in the correct mode (Edit Mode, Weight Paint Mode, etc).
When an operator's poll function fails within Python, an exception is raised.
For example, calling ``bpy.ops.view3d.render_border()`` from the console raises the following error:
@ -275,10 +260,10 @@ For example, calling ``bpy.ops.view3d.render_border()`` from the console raises
RuntimeError: Operator bpy.ops.view3d.render_border.poll() failed, context is incorrect
In this case the context must be the 3d view with an active camera.
In this case the context must be the 3D Viewport with an active camera.
To avoid using try/except clauses wherever operators are called you can call the operators
own ``poll()`` function to check if it can run in the current context.
To avoid using try-except clauses wherever operators are called, you can call the operators
own ``poll()`` function to check if it can run the operator in the current context.
.. code-block:: python
@ -291,11 +276,10 @@ Integration
Python scripts can integrate with Blender in the following ways:
- By defining a rendering engine.
- By defining a render engine.
- By defining operators.
- By defining menus, headers and panels.
- By inserting new buttons into existing menus, headers and panels
- By inserting new buttons into existing menus, headers and panels.
In Python, this is done by defining a class, which is a subclass of an existing type.
@ -306,56 +290,52 @@ Example Operator
.. literalinclude:: __/__/__/release/scripts/templates_py/operator_simple.py
Once this script runs, ``SimpleOperator`` is registered with Blender
and can be called from the operator search popup or added to the toolbar.
and can be called from Operator Search or added to the toolbar.
To run the script:
#. Highlight the above code then press :kbd:`Ctrl-C` to copy it.
#. Start Blender
#. Press :kbd:`Ctrl-Right` twice to change to the Scripting layout.
#. Click the button labeled ``New`` and the confirmation pop up in order to create a new text block.
#. Press :kbd:`Ctrl-V` to paste the code into the text panel (the upper left frame).
#. Click on the button **Run Script**.
#. Start Blender and switch to the Scripting workspace.
#. Click the *New* button in the text editor to create a new text data-block.
#. Copy the code from above and paste it into the text editor.
#. Click on the *Run Script* button.
#. Move your cursor into the 3D Viewport,
open the :ref:`operator search menu <blender_manual:bpy.ops.wm.search_menu>`,
open the :ref:`Operator Search menu <blender_manual:bpy.ops.wm.search_menu>`,
and type "Simple".
#. Click on the "Simple Operator" item found in search.
.. seealso::
.. seealso:: The class members with the ``bl_`` prefix are documented in the API
reference :class:`bpy.types.Operator`
The class members with the ``bl_`` prefix are documented in the API reference :class:`bpy.types.Operator`.
.. note::
The output from the ``main`` function is sent to the terminal;
in order to see this, be sure to :ref:`use the terminal <use_the_terminal>`.
Example Panel
-------------
Panels register themselves as a class, like an operator.
Panels are registered as a class, like an operator.
Notice the extra ``bl_`` variables used to set the context they display in.
.. literalinclude:: __/__/__/release/scripts/templates_py/ui_panel_simple.py
To run the script:
#. Highlight the above code then press :kbd:`Ctrl-C` to copy it.
#. Start Blender.
#. Click on the tab for the *Scripting* workspace.
#. Click the button labeled ``New`` to create a new text block.
#. Press :kbd:`Ctrl-V` to paste the code into the text panel (the upper left frame).
#. Click on the button **Run Script**.
#. Start Blender and switch to the Scripting workspace.
#. Click the *New* button in the text editor to create a new text data-block.
#. Copy the code from above and paste it into the text editor.
#. Click on the *Run Script* button.
To view the results:
#. Select the the default cube.
#. Select the default cube.
#. Click on the Object properties icon in the buttons panel (far right; appears as a tiny cube).
#. Scroll down to see a panel named **Hello World Panel**.
#. Changing the object name also updates **Hello World Panel's** Name: field.
#. Scroll down to see a panel named "Hello World Panel".
#. Changing the object name also updates *Hello World Panel's* name: field.
Note the row distribution and the label and properties that are available through the code.
Note the row distribution and the label and properties that are defined through the code.
.. seealso:: :class:`bpy.types.Panel`
@ -364,8 +344,7 @@ Types
=====
Blender defines a number of Python types but also uses Python native types.
Blender's Python API can be split up into 3 categories.
Blender's Python API can be split up into three categories.
Native Types
@ -374,7 +353,7 @@ Native Types
In simple cases returning a number or a string as a custom type would be cumbersome,
so these are accessed as normal Python types.
- Blender float/int/boolean -> float/int/boolean
- Blender float, int, boolean -> float, int, boolean
- Blender enumerator -> string
>>> C.object.rotation_mode = 'AXIS_ANGLE'
@ -393,11 +372,10 @@ so these are accessed as normal Python types.
Internal Types
--------------
Used for Blender data-blocks and collections: :class:`bpy.types.bpy_struct`
:class:`bpy.types.bpy_struct` is used for Blender data-blocks and collections.
Also for data that contains its own attributes: collections, meshes, bones, scenes, etc.
For data that contains its own attributes collections/meshes/bones/scenes... etc.
There are 2 main types that wrap Blenders data, one for data-blocks
There are two main types that wrap Blender's data, one for data-blocks
(known internally as ``bpy_struct``), another for properties.
>>> bpy.context.object
@ -406,14 +384,13 @@ There are 2 main types that wrap Blenders data, one for data-blocks
>>> C.scene.objects
bpy.data.scenes['Scene'].objects
Note that these types reference Blender's data so modifying them is immediately visible.
Note that these types reference Blender's data so modifying them is visible immediately.
Mathutils Types
---------------
Used for vectors, quaternion, eulers, matrix and color types, accessible from :mod:`mathutils`
Accessible from :mod:`mathutils` are vectors, quaternions, Euler angles, matrix and color types.
Some attributes such as :class:`bpy.types.Object.location`,
:class:`bpy.types.PoseBone.rotation_euler` and :class:`bpy.types.Scene.cursor_location`
can be accessed as special math types which can be used together and manipulated in various useful ways.
@ -422,14 +399,13 @@ Example of a matrix, vector multiplication:
.. code-block:: python
bpy.context.object.matrix_world * bpy.context.object.data.verts[0].co
bpy.context.object.matrix_world @ bpy.context.object.data.verts[0].co
.. note::
mathutils types keep a reference to Blender's internal data so changes can
be applied back.
Example:
.. code-block:: python
@ -449,13 +425,11 @@ Example of a matrix, vector multiplication:
Animation
=========
There are 2 ways to add keyframes through Python.
There are two ways to add keyframes through Python.
The first is through key properties directly, which is similar to inserting a keyframe from the button as a user.
The first is through key properties directly, which is like inserting a keyframe from the button as a user.
You can also manually create the curves and keyframe data, then set the path to the property.
Here are examples of both methods.
Both examples insert a keyframe on the active object's Z axis.
Here are examples of both methods. Both insert a keyframe on the active object's Z axis.
Simple example:
@ -467,7 +441,7 @@ Simple example:
obj.location[2] = 1.0
obj.keyframe_insert(data_path="location", frame=20.0, index=2)
Using Low-Level Functions:
Using low-level functions:
.. code-block:: python

130
doc/python_api/rst/info_tips_and_tricks.rst
View File

@ -4,23 +4,22 @@ Tips and Tricks
***************
Here are various suggestions that you might find useful when writing scripts.
Some of these are just Python features that scripters may not have thought to use with Blender,
others are Blender specific.
Some of these are just Python features that you may not have thought to use with Blender,
others are Blender-specific.
.. _use_the_terminal:
Use The Terminal
Use the Terminal
================
When writing Python scripts, it's useful to have a terminal open,
this is not the built-in Python console but a terminal application which is used to start Blender.
There are 3 main uses for the terminal, these are:
The three main use cases for the terminal are:
- You can see the output of ``print()`` as your script runs, which is useful to view debug info.
- The error trace-back is printed in full to the terminal which won't always generate an error popup in
- The error traceback is printed in full to the terminal which won't always generate an report message in
Blender's user interface (depending on how the script is executed).
- If the script runs for too long or you accidentally enter an infinite loop,
:kbd:`Ctrl-C` in the terminal (:kbd:`Ctrl-Break` on Windows) will quit the script early.
@ -28,26 +27,25 @@ There are 3 main uses for the terminal, these are:
.. note::
For Linux and macOS users this means starting the terminal first, then running Blender from within it.
On Windows the terminal can be enabled from the help menu.
On Windows the terminal can be enabled from the Help menu.
Interface Tricks
================
Access Operator Commands
------------------------
You may have noticed that the tooltip for menu items and buttons includes the ``bpy.ops.[...])`` command
You may have noticed that the tooltip for menu items and buttons includes the ``bpy.ops.[...]`` command
to run that button, a handy (hidden) feature is that you can press :kbd:`Ctrl-C` over
any menu item/button to copy this command into the clipboard.
any menu item or button to copy this command into the clipboard.
Access Data Path
----------------
To find the path from an :class:`ID` datablock to its setting isn't always so simple since it may be nested away.
To get this quickly you can right click on the setting and select select **Copy Data Path**,
To find the path from an :class:`ID` data-block to its setting isn't always so simple since it may be nested away.
To get this quickly open the context menu of the setting and select *Copy Data Path*,
if this can't be generated, only the property name is copied.
.. note::
@ -62,11 +60,10 @@ if this can't be generated, only the property name is copied.
Show All Operators
==================
While Blender logs operators in the Info space,
this only reports operators with the ``REGISTER`` option enabeld so as not to flood the *Info* view
While Blender logs operators in the Info editor,
this only reports operators with the ``REGISTER`` option enabled so as not to flood the *Info* view
with calls to ``bpy.ops.view3d.smoothview`` and ``bpy.ops.view3d.zoom``.
However, for testing it can be useful to see **every** operator called in a terminal,
Yet for testing it can be useful to see **every** operator called in a terminal,
do this by enabling the debug option either by passing the ``--debug-wm`` argument when starting Blender
or by setting :mod:`bpy.app.debug_wm` to ``True`` while Blender is running.
@ -74,20 +71,18 @@ or by setting :mod:`bpy.app.debug_wm` to ``True`` while Blender is running.
Use an External Editor
======================
Blenders text editor is fine for small changes and writing tests but its not full featured,
Blender's text editor is fine for small changes and writing tests but its not full featured,
for larger projects you'll probably want to use a standalone editor or Python IDE.
Editing a text file externally and having the same text open in Blender does work but isn't that optimal
so here are 2 ways you can easily use an external file from Blender.
Using the following examples you'll still need textblock in Blender to execute,
Editing a text file externally and having the same text open in Blender does work
but isn't that optimal so here are two ways you can use an external file from Blender.
Using the following examples you'll still need text data-block in Blender to execute,
but reference an external file rather than including it directly.
Executing External Scripts
--------------------------
This is the equivalent to running the script directly, referencing a scripts path from a 2 line text-block.
This is the equivalent to running the script directly, referencing a scripts path from a two line code block.
.. code-block:: python
@ -95,7 +90,7 @@ This is the equivalent to running the script directly, referencing a scripts pat
exec(compile(open(filename).read(), filename, 'exec'))
You might want to reference a script relative to the blend file.
You might want to reference a script relative to the blend-file.
.. code-block:: python
@ -128,9 +123,10 @@ has to call a function in the module, in this case ``main()`` but it can be any
an advantage with this is you can pass arguments to the function from this
small script which is often useful for testing different settings quickly.
The other issue with this is the script has to be in Pythons module search path.
While this is not best practice - for testing you can extend the search path,
this example adds the current blend files directory to the search path, then loads the script as a module.
The other issue with this is the script has to be in Python's module search path.
While this is not best practice -- for testing purposes you can extend the search path,
this following example adds the current blend-files directory to the search path
and then loads the script as a module.
.. code-block:: python
@ -148,42 +144,40 @@ this example adds the current blend files directory to the search path, then loa
myscript.main()
Don't Use Blender!
==================
While developing your own scripts Blenders interface can get in the way,
manually reloading, running the scripts, opening file import etc. adds overhead.
Use Blender without it's User Interface
=======================================
While developing your own scripts Blender's interface can get in the way,
manually reloading, running the scripts, opening file import, etc. adds overhead.
For scripts that are not interactive it can end up being more efficient not to use
Blenders interface at all and instead execute the script on the command line.
Blender's interface at all and instead execute the script on the command line.
.. code-block:: sh
blender --background --python myscript.py
You might want to run this with a blend file so the script has some data to operate on.
You might want to run this with a blend-file so the script has some data to operate on.
.. code-block:: sh
blender myscene.blend --background --python myscript.py
.. note::
Depending on your setup you might have to enter the full path to the Blender executable.
Once the script is running properly in background mode, you'll want to check the output of the script,
this depends completely on the task at hand however here are some suggestions.
this depends completely on the task at hand, however, here are some suggestions:
- render the output to an image, use an image viewer and keep writing over the same image each time.
- save a new blend file, or export the file using one of Blenders exporters.
- if the results can be displayed as text - print them or write them to a file.
- Render the output to an image, use an image viewer and keep writing over the same image each time.
- Save a new blend-file, or export the file using one of Blender's exporters.
- If the results can be displayed as text then print them or write them to a file.
While this can take a little time to setup, it can be well worth the effort
to reduce the time it takes to test changes - you can even have
to reduce the time it takes to test changes. You can even have
Blender running the script every few seconds with a viewer updating the results,
so no need to leave your text editor to see changes.
@ -200,7 +194,7 @@ but to quickly setup your own custom pipeline or writing one-off scripts this ca
Examples include:
- Run The Gimp in batch mode to execute custom scripts for advanced image processing.
- Run Gimp in batch mode to execute custom scripts for advanced image processing.
- Write out 3D models to use external mesh manipulation tools and read back in the results.
- Convert files into recognizable formats before reading.
@ -209,15 +203,16 @@ Bundled Python & Extensions
===========================
The Blender releases distributed from blender.org include a complete Python installation on all platforms,
this has the disadvantage that any extensions you have installed in your systems Python won't be found by Blender.
this has the disadvantage that any extensions you have installed on your system's Python environment
will not be found by Blender.
There are 2 ways around this:
There are two ways to work around this:
- Remove Blender Python sub-directory, Blender will then fallback on the systems Python and use that instead.
- Remove Blender Python subdirectory, Blender will then fallback on the system's Python and use that instead.
Depending on your platform,
you may need to explicitly reference the location of your Python installation using the
``PYTHONPATH`` environment variable, eg:
you may need to explicitly reference the location of your Python installation using
the ``PYTHONPATH`` environment variable, e.g:
.. code-block:: sh
@ -226,21 +221,21 @@ There are 2 ways around this:
.. warning::
The Python (major, minor) version must match the one that Blender comes with.
Therefor can't use Python 3.6 with Blender built to use Python 3.7.
Therefor you can't use Python 3.6 with Blender built to use Python 3.7.
- Copy or link the extensions into Blender's Python sub-directory so Blender can access them,
you could also copy the entire Python installation into Blenders sub-directory,
- Copy or link the extensions into Blender's Python subdirectory so Blender can access them,
you can also copy the entire Python installation into Blender's subdirectory,
replacing the one Blender comes with.
This works as long as the Python versions match and the paths are created in the same relative locations.
Doing this has the advantage that you can redistribute this bundle to others with Blender
including any extensions you rely on.
Drop Into a Python Interpreter in Your Script
=============================================
Insert a Python Interpreter into your Script
============================================
In the middle of a script you may want to inspect some variables,
run some function and generally dig about to see what's going on.
In the middle of a script you may want to inspect variables,
run functions and inspect the flow.
.. code-block:: python
@ -248,7 +243,7 @@ run some function and generally dig about to see what's going on.
code.interact(local=locals())
If you want to access both global and local variables do this...
If you want to access both global and local variables run this:
.. code-block:: python
@ -266,7 +261,7 @@ The next example is an equivalent single line version of the script above which
``code.interact`` can be added at any line in the script
and will pause the script an launch an interactive interpreter in the terminal,
and will pause the script to launch an interactive interpreter in the terminal,
when you're done you can quit the interpreter and the script will continue execution.
@ -279,13 +274,14 @@ The IPython prompt has auto-complete and some useful features that the standard
IPython.embed()
Admittedly this highlights the lack of any Python debugging support built into Blender, but its still handy to know.
Admittedly this highlights the lack of any Python debugging support built into Blender,
but its still a handy thing to know.
Advanced
========
Blender as a module
Blender as a Module
-------------------
From a Python perspective it's nicer to have everything as an extension
@ -293,26 +289,22 @@ which lets the Python script combine many components.
Advantages include:
- you can use external editors/IDE's with Blenders Python API and execute scripts within the IDE
- You can use external editors or IDEs with Blender's Python API and execute scripts within the IDE
(step over code, inspect variables as the script runs).
- editors/IDE's can auto complete Blender modules & variables.
- existing scripts can import Blender API's without having to run inside Blender.
- Editors or IDEs can auto-complete Blender modules and variables.
- Existing scripts can import Blender APIs without having to be run inside of Blender.
This is marked advanced because to run Blender as a Python module requires a special build option.
For instructions on building see
`Building Blender as a Python module <https://wiki.blender.org/wiki/Building_Blender/Other/BlenderAsPyModule>`_
`Building Blender as a Python module <https://wiki.blender.org/wiki/Building_Blender/Other/BlenderAsPyModule>`__.
Python Safety (Build Option)
----------------------------
Since it's possible to access data which has been removed (see Gotcha's),
this can be hard to track down the cause of crashes.
Since it's possible to access data which has been removed (see :doc:`Gotchas <info_gotcha>`),
can make it hard to track down the cause of crashes.
To raise Python exceptions on accessing freed data (rather than crashing),
enable the CMake build option ``WITH_PYTHON_SAFETY``.
This enables data tracking which makes data access about 2x slower
This enables data tracking which makes data access about two times slower
which is why the option isn't enabled in release builds.