code: def get_activities(self, before=None, after=None, limit=None):
          if before:
              before = self._utc_datetime_to_epoch(before)
          if after:
              after = self._utc_datetime_to_epoch(after)
          params = dict(before=before, after=after)
          result_fetcher = functools.partial(self.protocol.get,
                                             '/athlete/activities',
                                             **params)
          return BatchedResultsIterator(entity=model.Activity,
                                        bind_client=self,
                                        result_fetcher=result_fetcher,
                                        limit=limit)