# Script to delete all shapes where vertices only move a distance smaller than a given threshold.
#
# pruneLength and basisName should be defined by the user.
#
# This script assumes that all the shapes are relative to a single basis shape key.
# You must define the name of the basis shape key in basisName below.
# Alter pruneLength to give a threshold below which shape movement is ignored.
import bpy

def deleteShapeByName(obj, shapeName):

    iShape = obj.data.shape_keys.key_blocks.keys().index(shapeName)
    obj.active_shape_key_index = iShape
    bpy.ops.object.shape_key_remove()

###
# User-defined constants
basisName = 'Basis'
pruneLength = 0.0001
#

print('###')

bpy.ops.object.mode_set(mode='OBJECT')
obj = bpy.context.object
basisShape = obj.data.shape_keys.key_blocks[basisName]

shapesToDelete = []

numberOfShapes = len(obj.data.shape_keys.key_blocks)
# Find the names of shape keys where none of the keys move more than pruneLength
for shape in obj.data.shape_keys.key_blocks:
    noMovement = True
    if shape != basisShape:
        for v in obj.data.vertices:
            movement = (shape.data[v.index].co - basisShape.data[v.index].co).length
            if movement > pruneLength:
                noMovement = False
                break
        if noMovement:
            shapesToDelete.append(shape.name)

for shapeName in shapesToDelete:
    deleteShapeByName(obj, shapeName)

print(len(shapesToDelete), 'shape keys deleted from', numberOfShapes)