imports in test_warnings changes warnings.filters

[vstinner]

BPO	26742
Nosy	@vstinner, @vadmium
Superseder	bpo-18383: test_warnings modifies warnings.filters when running with "-W default"
Files	test_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 2016-05-22.04:42:01.755>
created_at = <Date 2016-04-13.00:51:35.119>
labels = []
title = 'imports in test_warnings changes warnings.filters'
updated_at = <Date 2016-05-22.04:42:01.753>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2016-05-22.04:42:01.753>
actor = 'martin.panter'
assignee = 'none'
closed = True
closed_date = <Date 2016-05-22.04:42:01.755>
closer = 'martin.panter'
components = []
creation = <Date 2016-04-13.00:51:35.119>
creator = 'vstinner'
dependencies = []
files = ['42449']
hgrepos = []
issue_num = 26742
keywords = ['patch']
message_count = 3.0
messages = ['263291', '263294', '266048']
nosy_count = 2.0
nosy_names = ['vstinner', 'martin.panter']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = None
status = 'closed'
superseder = '18383'
type = None
url = 'https://bugs.python.org/issue26742'
versions = ['Python 3.5', 'Python 3.6']

[vstinner]

---

$ ./python -Wd -m test -j0 test_warnings
Run tests in parallel using 6 child processes
0:00:01 [1/1] test_warnings
(...)
Warning -- warnings.filters was modified by test_warnings
1 test altered the execution environment:
    test_warnings
Total duration: 0:00:02

---

The problem are these two lines in test_warnings/init.py:
---

py_warnings = support.import_fresh_module('warnings', blocked=['_warnings'])
c_warnings = support.import_fresh_module('warnings', fresh=['_warnings'])

---

Each fresh "import warnings" calls _processoptions(sys.warnoptions) which can change warning filters.

Attached patch saves/restores warnings.filter to fix the resource warning from the test suite.

Note: the warning is not emited if tests are run sequentially (without the -jN option).

[vadmium]

Hmm your patch is a variation of the first patch in bpo-18383, and Serhiy’s comment about not fixing the underlying problem would apply: <https://bugs.python.org/issue18383#msg232451\>.

I can’t remember all the details now, but it sounds like Alex’s later patch may be a slightly more desirable hack :)

[vadmium]

I suggest to use the patch from bpo-18383.