docs: def dict_setdiff(dict_, negative_keys):
      r"""
      returns a copy of dict_ without keys in the negative_keys list
  
      Args:
          dict_ (dict):
          negative_keys (list):
      """
      keys = [key for key in six.iterkeys(dict_)
              if key not in set(negative_keys)]
      subdict_ = dict_subset(dict_, keys)
      return subdict_