code: def lookup_cell(self, uri):
          
          steps = uri.steps
          if steps[0] == '':
              found = self.root
              steps.popleft()
          else:
              found = self
          for step in steps:
              assert step != ''
              found = found.get_child(step)
              if not found:
                  break
              found = found._cell
          return found
docs: Looks up a local actor by its location relative to this actor.