code: def url_value_preprocessor(self, func: Callable, name: AppOrBlueprintKey=None) -> Callable:
          
          self.url_value_preprocessors[name].append(func)
          return func
docs: Add a url value preprocessor.
  
          This is designed to be used as a decorator. An example usage,
  
          .. code-block:: python
  
              @app.url_value_preprocessor
              def value_preprocessor(endpoint, view_args):
                  ...