web.py 文件源码

def _when_complete(self, result, callback):
        try:
            if result is None:
                callback()
            elif isinstance(result, Future):
                if result.done():
                    if result.result() is not None:
                        raise ValueError('Expected None, got %r' % result.result())
                    callback()
                else:
                    # Delayed import of IOLoop because it's not available
                    # on app engine
                    from tornado.ioloop import IOLoop
                    IOLoop.current().add_future(
                        result, functools.partial(self._when_complete,
                                                  callback=callback))
            else:
                raise ValueError("Expected Future or None, got %r" % result)
        except Exception as e:
            self._handle_request_exception(e)