code: def friendships_destroy(self, user_id=None, screen_name=None):
          
          params = {}
          set_str_param(params, 'user_id', user_id)
          set_str_param(params, 'screen_name', screen_name)
          return self._post_api('friendships/destroy.json', params)
docs: Allows the authenticating user to unfollow the specified user.
  
          https://dev.twitter.com/docs/api/1.1/post/friendships/destroy
  
          :param str user_id:
              The screen name of the user for whom to unfollow. Required if
              ``screen_name`` isn't given.
          :param str screen_name:
              The ID of the user for whom to unfollow. Required if ``user_id``
              isn't given.
  
          :returns:
              A dict containing the newly unfollowed user.