code: def _finish(self, g):
          
          assert g.ready()
  
          if g.successful():
              finished_tpart = g.get()
              self.wait_change.put(finished_tpart)
          else:
              self.wait_change.put(g.exception)
docs: Called on completion of an upload greenlet.
  
          Takes care to forward Exceptions or, if there is no error, the
          finished TarPartition value across a channel.