code: def _group_trace_frames(
          self, trace_frames: Iterable[TraceFrameQueryResult], limit: int
      ) -> Dict[Tuple[str, str], List[TraceFrameQueryResult]]:
          
          # pyre-fixme[9]: caller_buckets has type `DefaultDict[Tuple[str, str], List[T...
          caller_buckets: DefaultDict[
              Tuple[str, str], List[TraceFrameQueryResult]
          ] = defaultdict(list)
          for trace_frame in itertools.islice(trace_frames, limit):
              caller_buckets[(trace_frame.caller, trace_frame.caller_port)].append(
                  trace_frame
              )
          return caller_buckets
docs: Buckets together trace frames that have the same caller:caller_port.