code: def method_selector_fn(self):
          
          if callable(self.json_rpc_method):
              return self.json_rpc_method
          elif isinstance(self.json_rpc_method, (str,)):
              return lambda *_: self.json_rpc_method
          raise ValueError("``json_rpc_method`` config invalid.  May be a string or function")
docs: Gets the method selector from the config.