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How can I drive a shape key with a custom property slider using only Python scripting?

I intend to do a facial rig setup based on blendshapes and I want to do all the curves - shape key connections by scripting.

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Make an object custom property to drive each shape

From an Old blenderartists thread adds a custom property to context mesh object for each of its mesh data shapekeys, and sets up a driver from property to shapekey.

enter image description here

import bpy

context = bpy.context
scene = context.scene
object = context.object
mesh = object.data
shape_keys = mesh.shape_keys

frame = scene.frame_start
scene.frame_set(frame)
# dictionary of shape_key fcurves keyed by data_path
fcurve_dict = {}
rna = object.get('_RNA_UI', {})
for key, keyblock in shape_keys.key_blocks.items():
    if keyblock == shape_keys.key_blocks[0]:
        print("keyblock %s assumed Basis and ignored" % key)
        continue
    # create a custom property for the key

    rna[key] =  {"name": key,
                "min": keyblock.slider_min,
                "max": keyblock.slider_max,
                "description": "Shape Key %s" % key,
                "soft_min": keyblock.slider_min,
                "soft_max": keyblock.slider_max,
                }
    object[key] = keyblock.value
    object["_RNA_UI"] = rna

    # add a driver

    fcurve = shape_keys.driver_add('key_blocks["%s"].value' % key)
    driver = fcurve.driver
    driver.type = 'SCRIPTED'
    driver.expression = "shape"
    var = driver.variables.new()
    var.name = "shape"
    var.type = 'SINGLE_PROP'
    target = var.targets[0]
    target.id_type = "OBJECT"
    target.id = object.id_data
    target.data_path = '["%s"]' % key

If for instance you wish to put properties on the armature

object = bpy.data.objects["Name of Armature Object"]
mesh = bpy.data.meshes["Name of Mesh with Shapekeys"]

Please note old code.. don't use object as a variable name as its a reserved python keyword use ob or obj (for example) instead

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  • $\begingroup$ Thanks for your response. Its very helpfull. I have a question. isn't there a simpler code like putting : custom property is = shape key ? $\endgroup$ Commented Jan 24, 2020 at 18:36

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