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 respo…

Accepted Answer

`.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.

In what way is grequests asynchronous?

Solution

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