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In developer mode (-X dev), ResourceWarning is only emited once per line numbers #76270
Description
| BPO | 32089 |
|---|---|
| Nosy | @ncoghlan, @pitrou, @vstinner, @serhiy-storchaka |
| PRs |
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 2017-11-27.11:14:41.427>
created_at = <Date 2017-11-20.14:57:20.398>
labels = ['3.7']
title = 'In developer mode (-X dev), ResourceWarning is only emited once per line numbers'
updated_at = <Date 2017-11-27.11:14:41.426>
user = 'https://github.com/vstinner'bugs.python.org fields:
activity = <Date 2017-11-27.11:14:41.426>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2017-11-27.11:14:41.427>
closer = 'vstinner'
components = []
creation = <Date 2017-11-20.14:57:20.398>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 32089
keywords = ['patch']
message_count = 14.0
messages = ['306548', '306603', '306609', '306635', '306637', '306638', '306639', '306641', '306646', '306868', '306905', '306946', '307049', '307050']
nosy_count = 4.0
nosy_names = ['ncoghlan', 'pitrou', 'vstinner', 'serhiy.storchaka']
pr_nums = ['4482', '4584']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue32089'
versions = ['Python 3.7']
Activity
vstinner commentedon Nov 20, 2017
The -X dev mode currently *hides* some ResourceWarning warnings:
haypo@selma$ ./python -X dev x.py
x.py:2: ResourceWarning: unclosed file <_io.TextIOWrapper name='/etc/issue' mode='r' encoding='UTF-8'>
open('/etc/issue')
The problem is that the "-W default" inserted by -X dev overrides the final filter on ResourceWarning:
vstinner commentedon Nov 21, 2017
Attached PR 4482 fixes warnings filters:
haypo@selma$ ./python -X dev -c 'import warnings, pprint; pprint.pprint(warnings.filters)'
[('ignore', None, <class 'BytesWarning'>, None, 0),
('always', None, <class 'ResourceWarning'>, None, 0),
('default', None, <class 'Warning'>, None, 0)]
vstinner commentedon Nov 21, 2017
New changeset 09f3a8a by Victor Stinner in branch 'master':
bpo-32089: Fix warnings filters in dev mode (bpo-4482)
09f3a8a
pitrou commentedon Nov 21, 2017
I don't agree with this. You're comparing "-X dev" with a pydebug build of Python, not with a normal Python.
Your example shows the problem. If a program calls func() 1000 times in a row, they will show the same warning 1000 times. What does it bring to have the exact same warning (and line number) displayed 1000 times instead of once? Nothing. There is a reason the filter "default" isn't the same as "always", and it's that "always" can be completely overwhelming.
vstinner commentedon Nov 21, 2017
I don't know the rationale of the "always" action rather than "default". The choice was made 7 years ago, when Georg Brandl implemented the new ResourceWarning category: commit 08be72d.
The problem of ResourceWarning is that the warning logs where the last reference to the resource was cleared, or where the a garbage collection was triggered. Multiple resources can be created from different places, but all "die" at the same place.
In Python 3.6, I enhanced ResourceWarning to log also the traceback where the leaked resource has been created, if the tracemalloc is tracing memory allocations. When tracemalloc is used, it's useful to log ResourceWarning multiple times even if the warning itself is logged multipletimes. Well, that's an unusual usage of the ResourceWarning, we can also suggest to use -W always::ResourceWarning in that case.
In general, I would like to offer the same experience in "development mode" (-X dev) and with a pydebug build.
For ResourceWarning, your rationale only concerns pydebug build, no?
pitrou commentedon Nov 21, 2017
Le 21/11/2017 à 14:46, STINNER Victor a écrit :
Neither do I. But I don't think it matters a lot. pydebug builds are
almost only used by Python core developers. "developer mode" is target
at every Python developer.
If they have different names, they will be logged separately.
Why? I'm talking about "-X dev", not pydebug builds.
pitrou commentedon Nov 21, 2017
I forgot: the snippet above was made with "python -Wdefault::ResourceWarning".
serhiy-storchaka commentedon Nov 21, 2017
See also bpo-27535.
vstinner commentedon Nov 21, 2017
Antoine:
Oh wow, nice behaviour, I like it :-)
Antoine:
Oops sorry, typo (brain error), I mean: "also concerns".
Serhiy:
Oh, not leaking memory in warnings registies is a nice side effect of the "always" action :-)
--
It's much more complicated than what I expected to get the "correct behaviour" for warnings :-/
vstinner commentedon Nov 24, 2017
Antoine: What do you think of using the "default" action for pydebug build and -X dev?
pitrou commentedon Nov 24, 2017
That would be fine with me.
ncoghlan commentedon Nov 25, 2017
+1 from me for using "default" instead of "always" for ResourceWarning.
Folks can always combine "-X tracemalloc" with "-W always::ResourceWarning" if want to ensure they see absolutely every resource warning, rather than only representative ones.
vstinner commentedon Nov 27, 2017
New changeset 21c7730 by Victor Stinner in branch 'master':
bpo-32089: Use default action for ResourceWarning (bpo-4584)
21c7730
vstinner commentedon Nov 27, 2017
The "default warning filters" are documented, but only for Python compiled in release mode:
https://docs.python.org/dev/library/warnings.html#default-warning-filters
So I didn't touch this documentation.
The initial issue is now fixed: the development mode (-X dev) now behaves as the debug mode (pydebug build) for the default warning filters.
The second issue, Antoine's complain about the "always" action, was also fixed.
I close the issue. At the end, we should get a better debug experience ;-)