“async with” in Python 3.4

Question

The Getting Started docs for aiohttp give the following client example:

import asyncio
import aiohttp

async def fetch_page(session, url):
    with aiohttp.Timeo         


        

Answer 1

aiohttp's examples implemented using 3.4 syntax. Based on json client example your function would be:

@asyncio.coroutine
def fetch(session, url):
    with aiohttp.Timeout(10):
        resp = yield from session.get(url)
        try:
            return (yield from resp.text())
        finally:
            yield from resp.release()

Upd:

Note that Martijn's solution would work for simple cases, but may lead to unwanted behavior in specific cases:

@asyncio.coroutine
def fetch(session, url):
    with aiohttp.Timeout(5):
        response = yield from session.get(url)

        # Any actions that may lead to error:
        1/0

        return (yield from response.text())

# exception + warning "Unclosed response"

Besides exception you'll get also warning "Unclosed response". This may lead to connections leak in complex app. You will avoid this problem if you'll manually call resp.release()/resp.close():

@asyncio.coroutine
def fetch(session, url):
    with aiohttp.Timeout(5):
        resp = yield from session.get(url)
        try:

            # Any actions that may lead to error:
            1/0

            return (yield from resp.text())
        except Exception as e:
            # .close() on exception.
            resp.close()
            raise e
        finally:
            # .release() otherwise to return connection into free connection pool.
            # It's ok to release closed response:
            # https://github.com/KeepSafe/aiohttp/blob/master/aiohttp/client_reqrep.py#L664
            yield from resp.release()

# exception only

I think it's better to follow official examples (and __aexit__ implementation) and call resp.release()/resp.close() explicitly.