Deprecate-remove passing coroutine objects to asyncio.wait()

[1st1]

BPO	34790
Nosy	@rhettinger, @asvetlov, @serhiy-storchaka, @1st1, @miss-islington, @tirkarthi, @jack1142, @aeros
PRs	bpo-34790: Document how passing coroutines to asyncio.wait() can be confusing. #9543 [3.7] bpo-34790: [docs] Passing coroutines to asyncio.wait() can be confusing. (GH-9543) #9577 bpo-34790: Fix asyncio.wait() 3.8 whatsnew entry #16975 bpo-34790: Implement deprecation of passing coroutines to asyncio.wait() #16977 bpo-34790: add version of removal of explicit passing of coros to asyncio.wait's documentation #20008 bpo-34790: Remove passing coroutine objects to asyncio.wait() #31964

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2022-03-17.20:52:30.179>
created_at = <Date 2018-09-24.16:42:33.302>
labels = ['type-bug', 'expert-asyncio']
title = 'Deprecate-remove passing coroutine objects to asyncio.wait()'
updated_at = <Date 2022-03-17.20:52:30.179>
user = 'https://github.com/1st1'

bugs.python.org fields:

activity = <Date 2022-03-17.20:52:30.179>
actor = 'asvetlov'
assignee = 'none'
closed = True
closed_date = <Date 2022-03-17.20:52:30.179>
closer = 'asvetlov'
components = ['asyncio']
creation = <Date 2018-09-24.16:42:33.302>
creator = 'yselivanov'
dependencies = []
files = []
hgrepos = []
issue_num = 34790
keywords = ['patch']
message_count = 24.0
messages = ['326265', '326271', '326272', '326390', '326392', '326393', '326395', '326397', '355443', '355448', '355450', '355451', '355457', '355483', '355487', '355488', '355491', '355603', '355605', '355609', '355611', '359036', '368795', '415446']
nosy_count = 8.0
nosy_names = ['rhettinger', 'asvetlov', 'serhiy.storchaka', 'yselivanov', 'miss-islington', 'xtreak', 'jack1142', 'aeros']
pr_nums = ['9543', '9577', '16975', '16977', '20008', '31964']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue34790'
versions = []

[1st1]

asyncio.wait() accepts coroutines, wraps them into Tasks, and later returns those implicitly created Tasks in (done, pending) sets. This is very confusing to new asyncio users and it's almost impossible to figure out what is going on. See the first PR to the docs for more info.

Andrew, I think we should deprecate passing coroutines to asyncio.wait() in 3.8, and disallow that in 4.0.

[serhiy-storchaka]

4.0 is too far. Why not disallow them in 3.10?

[1st1]

4.0 is too far. Why not disallow them in 3.10?

What's the current plan? I thought it's going to be 3.8, 3.9, 4.0. Is there a PEP detailing this?

[1st1]

New changeset 996859a by Yury Selivanov in branch 'master':
bpo-34790: [docs] Passing coroutines to asyncio.wait() can be confusing. (GH-9543)
996859a

[1st1]

Actually, since Andrew also agrees that we need to deprecate passing coroutines to wait(), I'll keep this issue open until we add an actual DeprecationWarning in 3.8.

[miss-islington]

New changeset 3cc9557 by Miss Islington (bot) in branch '3.7':
bpo-34790: [docs] Passing coroutines to asyncio.wait() can be confusing. (GH-9543)
3cc9557

[1st1]

PendingDeprecationWarning

[serhiy-storchaka]

AFAIK there is no a plan for 4.0. But seems many core developers (including me) think that changing the major number should reflect some major changes like removing GIL. And Guido preferred 3.10 after 3.9.

[aeros]

Actually, since Andrew also agrees that we need to deprecate passing coroutines to wait(), I'll keep this issue open until we add an actual DeprecationWarning in 3.8.

Since 3.8 has been released and the deprecation notice is in the 3.8 whatsnew document, should we implement the warning in Lib/asyncio/tasks.py? If so, I can open a PR.

PendingDeprecationWarning

Also, it's not clear to me if this should be a DeprecationWarning or PendingDeprecationWarning. The most recent message from Yury in the issue suggests a PendingDeprecationWarning, but the actual entry in the documentation (https://docs.python.org/3/library/asyncio-task.html?highlight=asyncio%20wait#asyncio.wait) seems like it might imply that it would be a DeprecationWarning:

Deprecated since version 3.8: If any awaitable in aws is a coroutine, it is automatically scheduled as a Task. Passing coroutines objects to wait() directly is deprecated as it leads to confusing behavior.

[asvetlov]

I think we can add DeprecationWarning for 3.9.

Since it is a) just a warning b) already marked as deprecated in docs -- the harm is minimal.

Honestly, we just missed the issue when were prepared for 3.8

[aeros]

I think we can add DeprecationWarning for 3.9.

If we add the deprecation warning just for 3.9, would the removal release also be pushed forward?

Honestly, we just missed the issue when were prepared for 3.8

Yeah that's definitely understandable, there were quite a number of major changes made in 3.8. It was the first time I saw a deprecation clearly documented in a final release that didn't have an associated deprecation warning.

As for 3.8, I would like to update the whatsnew entry to add a link to this bpo issue if that's okay, as it does not at the moment. I recently included the entry in a PR that added entries for multiple significant changes for asyncio in the 3.8, but I forgot to include the bpo link (mostly because I found it in the documentation, rather than from the bpo issue).