docs: def _find_controller(self, class_):
          """Find first controller that matches given request class.
  
          Order is specified by the keys of
          ``SpaceTrackClient.request_controllers``
          (:class:`~collections.OrderedDict`)
          """
          for controller, classes in self.request_controllers.items():
              if class_ in classes:
                  return controller
          else:
              raise ValueError('Unknown request class {!r}'.format(class_))