Game Engine returns NONE when accessing object's .groupMembers attribute #40778

New Issue

Brian Cochran · 2014-06-24T02:59:17+02:00

Brian Cochran commented

2014-06-24 02:59:17 +02:00

System Information
Windows 7

Blender Version
Broken: 2.7 19e627c

Short description of error
When trying to access the object attribute .groupMembers, NONE is always returned. Only way it works is if you instance the group and put it on an active layer and try to access the group instance's attribute.

Exact steps for others to reproduce the error
Open the System Console and uncomment the print statements individually and run the Game Engine to see the bug. There are 4 different setups of accessing the attribute: 1.From object on Active layer. 2.From object on inactive layer 3.From group instance on active layer (This works currently). 4.From group instance on inactive layer.

BGE_bug.blend

**System Information** Windows 7 **Blender Version** Broken: 2.7 19e627c **Short description of error** When trying to access the object attribute .groupMembers, NONE is always returned. Only way it works is if you instance the group and put it on an active layer and try to access the group instance's attribute. **Exact steps for others to reproduce the error** Open the System Console and uncomment the print statements individually and run the Game Engine to see the bug. There are 4 different setups of accessing the attribute: 1.From object on Active layer. 2.From object on inactive layer 3.From group instance on active layer (This works currently). 4.From group instance on inactive layer. [BGE_bug.blend](https://archive.blender.org/developer/F95412/BGE_bug.blend)

Brian Cochran commented

2014-06-24 02:59:17 +02:00

Changed status to: 'Open'

Brian Cochran commented

2014-06-24 02:59:17 +02:00

Added subscriber: @BrianCochran

Inês Almeida commented

2014-06-25 23:41:03 +02:00

Added subscriber: @brita

Inês Almeida commented

2014-06-27 11:22:33 +02:00

Added subscribers: @kupoman, @Moguri

Inês Almeida commented

2014-06-27 11:22:33 +02:00

I see several things here. One, you are getting objects from the scene with both:

  scene.objects["obj_name"]
  scene.objectsInactive["obj_name"]

As far as I can tell, this is always getting the objects correctly including in the last case.

Then, having the object, you always query for groupMembers that, according to the documentation :
"Returns the list of group members if the object is a group object, otherwise None is returned."
So, doing this for the Cylinder and Cube is correctly returning None, as they belong to a group, but are not a group instance.
As I see it, this:

 scene.objects["Cube"].groupObject.groupMembers

should do what you want in that case.
But it doesn't because groupObject is returning None. I don't think this even makes much sense as an object can belong to several groups, so this should return a list? @kupoman @Moguri

Summing up the problems:
KX_GameObject.groupObject is returning None when it should return the group
KX_GameObject.groupObject should actually return a list??
KX_GameObject.groupMembers is returning None when the group instance is on an invisible layer, should it?

I see several things here. One, you are getting objects from the scene with both: ``` scene.objects["obj_name"] scene.objectsInactive["obj_name"] ``` As far as I can tell, this is always getting the objects correctly including in the last case. Then, having the object, you always query for groupMembers that, according to the [documentation ](http://www.blender.org/documentation/blender_python_api_2_71_release/bge.types.KX_GameObject.html#bge.types.KX_GameObject.groupMembers): "Returns the list of group members if the object is a group object, otherwise None is returned." So, doing this for the Cylinder and Cube is correctly returning None, as they belong to a group, but are not a group instance. As I see it, this: ``` scene.objects["Cube"].groupObject.groupMembers ``` should do what you want in that case. But it doesn't because groupObject is returning None. I don't think this even makes much sense as an object can belong to several groups, so this should return a list? @kupoman @Moguri Summing up the problems: KX_GameObject.groupObject is returning None when it should return the group KX_GameObject.groupObject should actually return a list?? KX_GameObject.groupMembers is returning None when the group instance is on an invisible layer, should it?

Inês Almeida commented

2014-06-27 12:04:15 +02:00

related commit: 7beff06950

related commit: 7beff06950

Mitchell Stokes commented

2014-07-01 06:16:58 +02:00

I think things are working as intended, but this is instead a case of confusing documentation. In the BGE, a KX_GroupObject is an object representing a dupligroup instance. So, only dupligroup instances will have a non-None groupMembers. Also, only objects that were instantiated from a dupligroup instance will have a non-None groupObject (in this sense, only one instance ever causes a specific object to be instantiated, so a list doesn't make sense). The only "groups" that the BGE cares about are dupligroup instances (it other wise doesn't recognize Blender groups).