Driver variable debugging value doesn't update if Scripted Expression is invalid #40897

New Issue

Garrett · 2014-06-30T23:55:36+02:00

Garrett commented

2014-06-30 23:55:36 +02:00

System Information
OS: Ubuntu 14.04
Linux kernel: 3.13.0-24-generic

Blender Version
Broken: blender-2.71-5588e45-linux-glibc211-x86_64

Short description of error

If you do not have a valid Scripted Expression for your driver, then the Value of the variables are not changed.

Exact steps for others to reproduce the error

Open the default .blend file
Select the cube, go to the N-menu and Add Single Driver, for example, to the x-location
Go to the Drivers context of the Graph Editor and open the N-menu for X-Location channel
Erase "0.000" from the Expr box so that we have a blank driver expression (or write an expression with an intentional error in it)
Set a variable to be the X location of the Camera (which has value 7.481)
Notice that the Value reported in the variable box will not get updated, but just display the last value it had (0.0)
Enter a valid driver expression (such as True), now the value in the variable box will start updating itself.

Here's a .blend with steps 1-5 completed: driver_var_prob.blend

**System Information** OS: Ubuntu 14.04 Linux kernel: 3.13.0-24-generic **Blender Version** Broken: blender-2.71-5588e45-linux-glibc211-x86_64 **Short description of error** If you do not have a valid Scripted Expression for your driver, then the Value of the variables are not changed. ![driver_bug.png](https://archive.blender.org/developer/F96146/driver_bug.png) **Exact steps for others to reproduce the error** 1) Open the default .blend file 2) Select the cube, go to the N-menu and Add Single Driver, for example, to the x-location 3) Go to the Drivers context of the Graph Editor and open the N-menu for X-Location channel 4) Erase "0.000" from the Expr box so that we have a blank driver expression (or write an expression with an intentional error in it) 5) Set a variable to be the X location of the Camera (which has value 7.481) 6) Notice that the Value reported in the variable box will not get updated, but just display the last value it had (0.0) 7) Enter a valid driver expression (such as True), now the value in the variable box will start updating itself. Here's a .blend with steps 1-5 completed: [driver_var_prob.blend](https://archive.blender.org/developer/F96148/driver_var_prob.blend)

Garrett commented

2014-06-30 23:55:36 +02:00

Changed status to: 'Open'

Garrett commented

2014-06-30 23:55:36 +02:00

Added subscriber: @Garrett-8

Joshua Leung commented

2014-07-01 01:30:34 +02:00

Changed status from 'Open' to: 'Archived'

Joshua Leung closed this issue

2014-07-01 01:30:34 +02:00

Joshua Leung self-assigned this 2014-07-01 01:30:34 +02:00

Joshua Leung commented

2014-07-01 01:30:34 +02:00

Not a bug. These only get evaluated when evaluating the driver gets evaluated, as there's no point doing so otherwise.

Garrett commented

2014-07-01 01:44:46 +02:00

I see. But it is pretty unexpected behavior.

This was a simple example, but I was working with a more complicated scripted expression that also used a custom property in it. I could not figure out what was wrong with my expression, but when I saw that it was displaying the incorrect value for my custom property, I assumed there was some issue with the custom property.

It just seems like Debug Info is not very helpful if it's incorrect when there actually is a bug in your scripted expression.

I see. But it is pretty unexpected behavior. This was a simple example, but I was working with a more complicated scripted expression that also used a custom property in it. I could not figure out what was wrong with my expression, but when I saw that it was displaying the incorrect value for my custom property, I assumed there was some issue with the custom property. It just seems like Debug Info is not very helpful if it's incorrect when there actually is a bug in your scripted expression.

Garrett commented

2014-07-01 01:49:07 +02:00

Now that I'm aware of this, it won't throw me off again, but I still think other users could get confused by this.

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Driver variable debugging value doesn't update if Scripted Expression is invalid #40897