code: def context_register(self, func, *args):
          
          token = self.register(func, *args)
          try:
              yield
          finally:
              self.unregister(token)
docs: :term:`Context manager <context manager>` which temporarily registers a
          filter function.
  
          :param func: The filter function to register.
          :param order: The sorting key for the filter function.
          :rtype: :term:`context manager`
          :return: Context manager which temporarily registers the filter
                   function.
  
          If :meth:`register` does not require `order` because it has been
          overridden in a subclass, the `order` argument can be omitted here,
          too.
  
          .. versionadded:: 0.9