code: def _backoff(self, context):
          # type: (ExponentialRetryWithMaxWait,
          #        azure.storage.common.models.RetryContext) -> int
          
          self._backoff_count += 1
          if self._backoff_count == 1:
              self._last_backoff = self.initial_backoff
          else:
              self._last_backoff *= 2
          if self._last_backoff > self.max_backoff and self.reset_at_max:
              self._backoff_count = 1
              self._last_backoff = self.initial_backoff
          return self._last_backoff
docs: Backoff calculator
          :param ExponentialRetryWithMaxWait self: this
          :param azure.storage.common.models.RetryContext context: retry context
          :rtype: int
          :return: backoff amount