code: def _get_stream_handle_ids(self, handles):
          
          stream_handle_ids = defaultdict(dict)
          for stream in self.streams:
              for h in self.models:
                  if h in handles:
                      handle_id = handles[h].ref['id']
                      stream_handle_ids[stream][h] = handle_id
          return stream_handle_ids
docs: Gather the ids of the plotting handles attached to this callback
          This allows checking that a stream is not given the state
          of a plotting handle it wasn't attached to