code: def _CallMethod(self, srvc, method_descriptor,
                    rpc_controller, request, callback):
      
      if method_descriptor.containing_service != self.descriptor:
        raise RuntimeError(
            'CallMethod() given method descriptor for wrong service type.')
      method = getattr(srvc, method_descriptor.name)
      return method(rpc_controller, request, callback)
docs: Calls the method described by a given method descriptor.
  
      Args:
        srvc: Instance of the service for which this method is called.
        method_descriptor: Descriptor that represent the method to call.
        rpc_controller: RPC controller to use for this method's execution.
        request: Request protocol message.
        callback: A callback to invoke after the method has completed.