How to create a PyDriver in blender 2.7

Question

I've heard of PyDrivers where you can put python code into a driver, & I'm wondering, how would you do that in blender 2.7x without resorting to a lower blender version?

Here's what I'd like to put in the driver:

(ob(‘Armature’).getPose().bones[‘Bone.001’].head - ob(‘Armature’).getPose().bones[‘Bone’].head).length/250

i think it's the same as normal driver just use 'scripted expression' — Chebhou, Mar 12 '15 at 18:54
I've tried putting in a short python script in the expression field when using 'scripted expression' but then I get an 'Invalid Python Expression' error — ISaenz, Mar 12 '15 at 19:06
@ISaenz Your only supposed to write a one line snippet - I think that's why you get an error — someonewithpc, Mar 12 '15 at 19:56

score 8 · Answer 1 · edited Feb 10 '19 at 06:40

your example can be implemented as in the following driver :

enter image description here

but for more complex drivers refer to this DOC page , the important part is that you can define your function and add it to driver namespace as in this example :

import bpy

def driverFunc(val):

    return val * val    # return val squared

bpy.app.driver_namespace['driverFunc'] = driverFunc    # add function to driver_namespace

now you can use it the driver scripted expression

How to create a PyDriver in blender 2.7

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