code: def _remove_call(self, real_time, call):
          
          try:
              (delayed_call, calls) = self._buckets[real_time]
          except KeyError:
              # no such bucket ... error? swallow?
              return
          # remove call; if we're empty, cancel underlying
          # bucket-timeout IDelayedCall
          calls.remove(call)
          if not calls:
              del self._buckets[real_time]
              delayed_call.cancel()
docs: Internal helper. Removes a (possibly still pending) call from a
          bucket. It is *not* an error of the bucket is gone (e.g. the
          call has already happened).