-W command line options should have higher priority than PYTHONWARNINGS environmental variable

[Arfrever]

BPO	20355
Nosy	@warsaw, @brettcannon, @pitrou, @larryhastings, @pjenvey, @ezio-melotti, @merwok, @briancurtin, @serhiy-storchaka
Dependencies	bpo-20373: Use test.script_helper.assert_python_ok() instead of subprocess.* in test.test_warnings
Files	python-warnings.patch

^{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 2014-04-28.22:58:46.484>
created_at = <Date 2014-01-22.21:41:46.788>
labels = ['interpreter-core', 'type-feature']
title = '-W command line options should have higher priority than PYTHONWARNINGS environmental variable'
updated_at = <Date 2014-04-28.22:58:46.482>
user = 'https://bugs.python.org/Arfrever'

bugs.python.org fields:

activity = <Date 2014-04-28.22:58:46.482>
actor = 'pitrou'
assignee = 'none'
closed = True
closed_date = <Date 2014-04-28.22:58:46.484>
closer = 'pitrou'
components = ['Interpreter Core']
creation = <Date 2014-01-22.21:41:46.788>
creator = 'Arfrever'
dependencies = ['20373']
files = ['33673']
hgrepos = []
issue_num = 20355
keywords = ['patch']
message_count = 13.0
messages = ['208854', '208856', '208886', '209018', '209022', '209026', '209028', '209031', '209089', '209090', '212094', '217437', '217438']
nosy_count = 11.0
nosy_names = ['barry', 'brett.cannon', 'pitrou', 'larry', 'pjenvey', 'ezio.melotti', 'eric.araujo', 'Arfrever', 'brian.curtin', 'python-dev', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue20355'
versions = ['Python 3.5']

[Arfrever]

Currently Python has non-intuitive behavior such that PYTHONWARNINGS environmental variable has higher priority than -W command line options.

$ python3.4 -c '__import__("warnings").warn("xxx", DeprecationWarning)'
$ python3.4 -Wd -c '__import__("warnings").warn("xxx", DeprecationWarning)'
-c:1: DeprecationWarning: xxx
$ python3.4 -We -c '__import__("warnings").warn("xxx", DeprecationWarning)'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
DeprecationWarning: xxx
$ PYTHONWARNINGS="e" python3.4 -Wd -c '__import__("warnings").warn("xxx", DeprecationWarning)'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
DeprecationWarning: xxx
$ PYTHONWARNINGS="d" python3.4 -We -c '__import__("warnings").warn("xxx", DeprecationWarning)'
-c:1: DeprecationWarning: xxx
$

I think that settings from -W command line options should have higher priority than PYTHONWARNINGS environmental variable.

(Adding people from issue bpo-7301 to nosy list.)

[pitrou]

Agreed.

[Arfrever]

The attached patch moves calls to PySys_AddWarnOption* for -W options to after parsing PYTHONWARNINGS.

I think that this bug fix could be applied in Python 3.4. The patch does not introduce any failures in full test suite.

[pitrou]

Well, 3.4 isn't supposed to receive behaviour changes anymore, unless Larry says it's ok.

[pitrou]

About the patch (note the code review tool hasn't accepted it, so I'm commenting here):

• in the tests, I think comparing stderr as-is will fail under Windows, where the line separator is b"\r\n"; better call splitlines() first
• in the tests, I think it would be better to use test.script_helper.assert_python_ok() (it will automate some stuff for you), even though other tests don't in that file
• in main.c, you need to Py_DECREF warning_options when you are done with it.

[larryhastings]

Is this behavior causing problems? How bad is it?

Can I get more opinions about this than just Arfrever and Antoine? Not that I don't trust their opinions, I just want to see a larger sample size.

[pitrou]

Is this behavior causing problems? How bad is it?

Not really. It's just a bit suboptimal and counter-intuitive
(local settings should trump global settings).

[Arfrever]

The new patch includes changes suggested by Antoine. (This patch should be applied after patch from issue bpo-20373.)

[brettcannon]

I agree with Antoine; this can wait for Python 3.5.

[larryhastings]

Okay, then yes, let's save this for 3.5. Thanks!

[serhiy-storchaka]

Final patch should remove a workaround in Tools/scripts/run_tests.py.