code: def _process_table(self, cache=True):
          
          table = self.source()
          assert not isinstance(table, None.__class__), \
              "{}.source needs to return something, not None".format(self.__class__.__name__)
          table = post_process(table, self.post_processors())
          if cache:
              self.to_cache(table)
          return table
docs: Applies the post processors