code: def process(self, tup):
          
          # Append latest Tuple to batches
          group_key = self.group_key(tup)
          self._batches[group_key].append(tup)
docs: Group non-tick Tuples into batches by ``group_key``.
  
          .. warning::
              This method should **not** be overriden.  If you want to tweak
              how Tuples are grouped into batches, override ``group_key``.