Set Driver Target Object from the Console

Question

Setting a Target Object for a constraint is fairly straight forward:

path = bpy.data.objects["Nurbspath"]
bpy.data.objects["Armature"].pose.bones["Bone"].constraints["Follow Path"].target = path

I'm still very new to this and I can't figure out how to do the same thing for a driver. Specifically I would like to be able to set a the Target Object for a specific variable of a specific Driver from the console. I think it would go something like this:

path = bpy.data.objects["NurbsPath"]
bpy.data.objects["Armature"].animation_data.drivers.driver.driver.variables.var["var"].targets.driver_target.ID = path

But as far as I can tell drivers don't have names so how does one specify them?

The python tooltip isn't particularly helpful either...

bpy.data.objects["Armature"] ... id

Thanks for your assistance.

Answer 1

Working with drivers in Python isn't necessarily fun, unless you also create them directly from your script. If you do that, you can catch the driver objects as return values from the creation function, and use that object to create variables, set targets, and whatnot. Here is a quick example for how to do this:

import bpy

# get the objects from the scene
path = bpy.data.objects.get("NurbsCurve")
arm = bpy.data.objects.get("Armature")

# if both exist, create the driver
if path and arm:
    print('Objects exist, continuing by adding driver')

    # create a driver for all location channels
    drv_x, drv_y, drv_z = arm.pose.bones['Bone'].driver_add('location')

    # set the driver type to MAXIMUM_VALUE
    drv_x.driver.type='MAX'

    # create a variable to control something
    var = drv_x.driver.variables.new()

    # set the target object to the NURBS path
    # note that targets is a list, depending on the driver type more than one value
    # could be required
    var.targets[0].id = path

    # set the target property to the x location of that path object
    var.targets[0].data_path='location.x'

Note that I'm also unpacking the list to drv_x, drv_y and drv_z. This is just a way of naming the three driver objects directly at creation time. If you catch the result in one object called drv, you can access the driver for the X location by using an index: drv[0].

Regarding the Python Tooltip, the line above the one you quoted is actually more helpful: It says DriverTarget.id. This tells you that the object needs to be of type DriverTarget, then you'll find an id property on it. var.targets[0] is of such a type.

Answer 2

You'll want to use .find(data_path, index=index) on Object().animation_data.drivers, to avoid having to remake the driver.

data_path is the RNA path of the driven value, relative to the Object(). index is the driven index for array/vector properties.

So, for example, to change the target of a variable on a driver which controls an object's Y location transform channel, you'd do:

YourObject.animation_data.drivers.find('location', index=1).driver.variables["YourVariableName"].targets[0].id = NewTargetObject

Note that the AnimDataDrivers.find() is documented as performing a linear scan, so it's probably equivalent in performance to manually checking .data_path and .array_index on all drivers until you find the right one.