docs: def setattr_path(obj, path, value):
      """
      Set an attribute path, as defined by a string separated by '__'.
      setattr_path(foo, 'a__b__c', value) is equivalent to "foo.a.b.c = value".
      """
      path = path.split('__')
      o = obj
      for name in path[:-1]:
          o = getattr(o, name)
      setattr(o, path[-1], value)
      return obj