docs: def get_friends_list(self, steamID, relationship='all', format=None):
          """Request the friends list of a given steam ID filtered by role.
  
          steamID: The user ID
          relationship: Type of friend to request (all, friend)
          format: Return format. None defaults to json. (json, xml, vdf)
  
          """
          parameters = {'steamid' : steamID, 'relationship' : relationship}
          if format is not None:
              parameters['format'] = format
          url = self.create_request_url(self.interface, 'GetFriendsList', 1,
              parameters)
          data = self.retrieve_request(url)
          return self.return_data(data, format=format)