docs: def extend(instance, new_class):
      """Adds new_class to the ancestors of instance.
  
      :param instance: Instance that will have a new ancestor.
      :param new_class: Ancestor.
      """
      instance.__class__ = type(
          '%s_extended_with_%s' % (instance.__class__.__name__, new_class.__name__),
          (new_class, instance.__class__,),
          {}
      )