Can't call result() on futures in tornado

Question

I want to do some asynchronous HTTP-requests using the python library tornado (version 4.2). I can however not force a future to complete (using result()) since

Answer 1

Try to create another Future and use add_done_callback:

From Tornado documentation

from tornado.concurrent import Future

def async_fetch_future(url):
    http_client = AsyncHTTPClient()
    my_future = Future()
    fetch_future = http_client.fetch(url)
    fetch_future.add_done_callback(
        lambda f: my_future.set_result(f.result()))
    return my_future

But you still need solve the future with the ioloop, like this:

# -*- coding: utf-8 -*-
from tornado.concurrent import Future
from tornado.httpclient import AsyncHTTPClient
from tornado.ioloop import IOLoop


def async_fetch_future():
    http_client = AsyncHTTPClient()
    my_future = Future()
    fetch_future = http_client.fetch('http://www.google.com')
    fetch_future.add_done_callback(
        lambda f: my_future.set_result(f.result()))
    return my_future

response = IOLoop.current().run_sync(async_fetch_future)

print(response.body)

Another way to this, is using tornado.gen.coroutinedecorator, like this:

# -*- coding: utf-8 -*-
from tornado.gen import coroutine
from tornado.httpclient import AsyncHTTPClient
from tornado.ioloop import IOLoop


@coroutine
def async_fetch_future():
    http_client = AsyncHTTPClient()
    fetch_result = yield http_client.fetch('http://www.google.com')
    return fetch_result

result = IOLoop.current().run_sync(async_fetch_future)

print(result.body)

coroutine decorator causes the function to return a Future.