code: def unregister(self, token_to_remove):
          
          for i, (_, token, _) in enumerate(self._filter_order):
              if token == token_to_remove:
                  break
          else:
              raise ValueError("unregistered token: {!r}".format(
                  token_to_remove))
          del self._filter_order[i]
docs: Unregister a filter function.
  
          :param token_to_remove: The token as returned by :meth:`register`.
  
          Unregister a function from the filter chain using the token returned by
          :meth:`register`.