MuteAllShapekeys.py

import bpy

context = bpy.context
if context.active_object:
    obj = context.active_object
    if obj.data.shape_keys:
        for shape_key in obj.data.shape_keys.key_blocks:
            shape_key.mute = True
    else:
        self.report({'ERROR'}, "The active object has no shapekeys.")
else:
    self.report({'ERROR'}, "Please select an object before running the script.")