New submission from Daisuke Miyakawa: I was reading the following doc and got confused.
https://docs.python.org/3.7/reference/datamodel.html#object.__aenter__ According to the API doc itself (and original PEP 492), __aenter__() "is semantically similar to the __enter__(), with only difference that it must return an awaitable." __aexit__() has similar sentence that confuses me too. PEP 492 also implies the (awaitable) object returned from obj.__aenter__() will be awaited immediately. In same manner, the (awaitable) object returned from obj.__aexit__() will be awaited too. (From PEP 492) > async with EXPR as VAR: > BLOCK > > which is semantically equivalent to: > > mgr = (EXPR) > aexit = type(mgr).__aexit__ > aenter = type(mgr).__aenter__(mgr) > exc = True > > VAR = await aenter > try: > BLOCK > except: > if not await aexit(mgr, *sys.exc_info()): > raise > else: > await aexit(mgr, None, None, None) On the other hand, actual CPython implementation won't do that; it won't await the returned objects. Moreover, the example shown in the API doc (AsyncContextManager) does NOT return awaitable as the doc itself suggests, but just await inside __aenter__() (and __aexit__()). > class AsyncContextManager: > async def __aenter__(self): > await log('entering context') > > async def __aexit__(self, exc_type, exc, tb): > await log('exiting context') I'm not sure which is true; the doc saying "__aenter__() must return awaitable" is just incorrect, or CPython implementation has a bug. Actual source implies former. _ContextManagerMixin in asyncio.locks does not return awaitable at all, for example. Anyway, I believe there are inconsistencies around here. ---------- assignee: docs@python components: Documentation messages: 297542 nosy: dmiyakawa, docs@python priority: normal severity: normal status: open title: Inconsistent or wrong documentation around Asynchronous Context Manager versions: Python 3.6, Python 3.7 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue30831> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
