How to wrap asynchronous and gen functions together in Tornado?

How to wrap asynchronous and gen functions together in Tornado? My code looks like below, the error is 'Future' object has no attribute 'body'.

Did I place the decorators in a wrong way?

import tornado.httpclient
import tornado.web
import tornado.gen
import tornado.httpserver
import tornado.ioloop

class Class1(tornado.web.RequestHandler):

    @tornado.web.asynchronous
    def post(self, *args, **kwargs):
        url = self.get_argument('url', None)
        response = self.json_fetch('POST', url, self.request.body)
        self.write(response.body)
        self.finish()

    @tornado.gen.engine
    def json_fetch(self, method, url, body=None, *args, **kwargs):
        client = tornado.httpclient.AsyncHTTPClient()
        headers = tornado.httputil.HTTPHeaders({"content-type": "application/json charset=utf-8"})
        request = tornado.httpclient.HTTPRequest(url, method, headers, body)
        yield tornado.gen.Task(client.fetch, request)

Solution

You don't need "asynchronous" in this code example. "gen.engine" is obsolete, use "coroutine" instead. You don't generally need to use "gen.Task" much these days, either. Make four changes to your code:

Wrap "post" in "coroutine"
"yield" the result of self.json_fetch instead of using the result directly.
No need to call "finish" in a coroutine, Tornado finishes the response when a coroutine completes.
Wrap json_fetch in "coroutine", too.

The result:

class ClubCreateActivity(tornado.web.RequestHandler):

    @tornado.gen.coroutine
    def post(self, *args, **kwargs):
        url = self.get_argument('url', None)
        response = yield self.json_fetch('POST', url, self.request.body)
        self.write(response.body)

    @tornado.gen.coroutine
    def json_fetch(self, method, url, body=None, *args, **kwargs):
        client = tornado.httpclient.AsyncHTTPClient()
        headers = tornado.httputil.HTTPHeaders({"content-type": "application/json charset=utf-8"})
        request = tornado.httpclient.HTTPRequest(url, method, headers, body)
        response = yield client.fetch(request)
        raise gen.Return(response)