In what way is grequests asynchronous?

Question

I've been using the python requests library for some time, and recently had a need to make a request asynchronously, meaning I would like to send off the HTTP request, have my main thread continue to execute, and have a callback called when the request returns.

Naturally, I was lead to the grequests library (https://github.com/kennethreitz/grequests), but i'm confused about the behavior. For example:

import grequests

def print_res(res):
    from pprint import pprint
    pprint (vars(res))

req = grequests.get('http://www.codehenge.net/blog', hooks=dict(response=print_res))
res = grequests.map([req])

for i in range(10):
    print i

The above code will produce the following output:

<...large HTTP response output...>

0
1
2
3
4
5
6
7
8
9

The grequests.map() call obviously blocks until the HTTP response is available. It seems likely I misunderstood the 'asynchronous' behavior here, and the grequests library is just for performing multiple HTTP requests concurrently and sending all responses to a single callback. Is this accurate?

Answer 1

.map() is meant to run retrieval of several URLs in parallel, and will indeed wait for these tasks to complete (gevent.joinall(jobs)) is called).

Use .send() instead to spawn jobs, using a Pool instance:

req = grequests.get('http://www.codehenge.net/blog', hooks=dict(response=print_res))
job = grequests.send(req, grequests.Pool(1))

for i in range(10):
    print i

Without the pool the .send() call will block still, but only for the gevent.spawn() call it executes.