Add async_timeout decorator

[mosquito]

New async_timeout decorator.

class TimedOutTestCase(TestCase):
    @async_timeout
    async def test_default_timeout(self):
        await asyncio.sleep(999, loop=self.loop)

    @async_timeout(seconds=1)
    async def test_custom_timeout(self):
        await asyncio.sleep(999, loop=self.loop)

[Martiusweb]

Hi,

Thanks for you contribution. Can you explain why you want to introduce this feature and in which case it is useful for you?

Thanks

[mosquito]

Often some tests got stuck. For example future was created without loop= parameter or other dummy errors. In this case you have to wait CI timeout or cancel jobs manually.

[Martiusweb]

It can be useful to have a timeout set on each test, but I feel that your proposal of a decorator targets a use case too broad to be included in asynctest as it is: this should be in a "utils" library (or maybe even in asyncio itself).

What do you think?

[mosquito]

Hmm... In my cases it's so useful for tests. But you are right, that's a common implementation. Actually I was inspired by gen_test decorator from tornado.

[Kentzo]

With the async_timeout package decorator could be implemented like this:

...
    DEFAULT_ASYNC_TIMEOUT = 1.0

    @classmethod
    def with_timeout(cls, timeout=None):
        if timeout is None:
            timeout = cls.DEFAULT_ASYNC_TIMEOUT

        def decorator(coro):
            @functools.wraps(coro)
            async def wrapper(*args, **kwargs):
                with async_timeout.timeout(timeout):
                    await coro(*args, **kwargs)

            return wrapper

        return decorator
...