asyncio docs refer to wrong TimeoutError

[qmega]

BPO	21376
Nosy	@gvanrossum, @pitrou, @vstinner, @giampaolo, @1st1

^{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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assignee = None
closed_at = <Date 2014-05-28.22:06:16.801>
created_at = <Date 2014-04-28.18:05:57.039>
labels = ['library', 'docs']
title = 'asyncio docs refer to wrong TimeoutError'
updated_at = <Date 2014-05-28.22:06:16.800>
user = 'https://bugs.python.org/qmega'

bugs.python.org fields:

activity = <Date 2014-05-28.22:06:16.800>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2014-05-28.22:06:16.801>
closer = 'vstinner'
components = ['Documentation', 'Library (Lib)']
creation = <Date 2014-04-28.18:05:57.039>
creator = 'qmega'
dependencies = []
files = []
hgrepos = []
issue_num = 21376
keywords = []
message_count = 5.0
messages = ['217390', '217400', '217402', '219310', '219311']
nosy_count = 8.0
nosy_names = ['gvanrossum', 'pitrou', 'vstinner', 'giampaolo.rodola', 'docs@python', 'python-dev', 'yselivanov', 'qmega']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue21376'
versions = ['Python 3.4', 'Python 3.5']

[qmega]

Example: https://docs.python.org/3.4/library/asyncio-task.html
TimeoutError is mentioned several times, and links to the OSError subclass. However, the actual TimeoutError raised by asyncio stuff is the one from concurrent.futures, which is not compatible. The docs as they are seem to suggest that something like "except TimeoutError" would be appropriate, when in fact that would not produce the expected behavior; "except asyncio.TimeoutError" is what you'd want.

[pitrou]

Gasp. Perhaps concurrent.futures.TimeoutError can inherit from the standard TimeoutError? The following patch doesn't seem to disrupt the test suite:

diff --git a/Lib/concurrent/futures/_base.py b/Lib/concurrent/futures/_base.py
--- a/Lib/concurrent/futures/_base.py
+++ b/Lib/concurrent/futures/_base.py
@@ -49,7 +49,7 @@ class CancelledError(Error):
     """The Future was cancelled."""
     pass
 
-class TimeoutError(Error):
+class TimeoutError(Error, TimeoutError):
     """The operation exceeded the given deadline."""
     pass

[gvanrossum]

I considered this, and decided against unifying the two TimeoutErrors.

First the builtin TimeoutError is specifically a subclass of OSError representing the case where errno is ETIMEDOUT. But asyncio.TimeoutError means nothing of the sort.

Second, the precedent is concurrent.futures.TimeoutError. The asyncio one is used under the same conditions as that one.

I think we should just update the links in the docs to be correct.

[python-dev]

New changeset 6d90e8df01f4 by Victor Stinner in branch '3.4':
Issue bpo-21376: document asyncio.TimeoutError
http://hg.python.org/cpython/rev/6d90e8df01f4

New changeset 03bb1077b362 by Victor Stinner in branch 'default':
(Merge 3.4) Issue bpo-21376: document asyncio.TimeoutError
http://hg.python.org/cpython/rev/03bb1077b362

[vstinner]

Thanks for the report. In fact, asyncio.TimeoutError was not documented at all. It should now be fixed.