uncaught exception in lib/warnings.py when executed with pythonw

[stockbsd]

BPO	23016
Nosy	@vstinner, @serhiy-storchaka
Files	warnings_stderr_none.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 = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2014-12-10.22:08:57.215>
created_at = <Date 2014-12-09.01:27:03.159>
labels = ['type-bug', 'library']
title = 'uncaught exception in lib/warnings.py when executed with pythonw'
updated_at = <Date 2014-12-14.08:58:48.377>
user = 'https://bugs.python.org/stockbsd'

bugs.python.org fields:

activity = <Date 2014-12-14.08:58:48.377>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2014-12-10.22:08:57.215>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2014-12-09.01:27:03.159>
creator = 'stockbsd'
dependencies = []
files = ['37396']
hgrepos = []
issue_num = 23016
keywords = ['patch']
message_count = 10.0
messages = ['232342', '232369', '232371', '232374', '232391', '232424', '232443', '232631', '232632', '232633']
nosy_count = 5.0
nosy_names = ['vstinner', 'Arfrever', 'python-dev', 'serhiy.storchaka', 'stockbsd']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue23016'
versions = ['Python 2.7', 'Python 3.4', 'Python 3.5']

[stockbsd]

in py3k, the following simple code will throw an uncatched exception when executed with pythonw:

import warnings
warnings.warn('test')

the problem occurs in showarning function: in py3k's pythonw , stderr/stdout is set to None, so the file.write(...) statement will thorw AttributeError uncatched. I think a catch-all except(delete 'OSError') can solve this.

def showwarning(message, category, filename, lineno, file=None, line=None):
    """Hook to write a warning to a file; replace if you like."""
    if file is None:
        file = sys.stderr
    try:
        file.write(formatwarning(message, category, filename, lineno, line))
    except OSError:
        pass # the file (probably stderr) is invalid - this warning gets lost.

[serhiy-storchaka]

Here is a patch. 2.7 is affected too.

[stockbsd]

1. py2 is unaffected, because stderr/stdout is not None in py2's pythonw and the catch works correctly.

2. as to py3, I prefer this patch:

• execpt OSError:
  + execpt:

[vstinner]

+ execpt:

Please never use that, but "except Exception:" instead to not catch SystemExit or KeyboardInterrupt.

[serhiy-storchaka]

I afraid this will silence unexpected errors.

[vstinner]

warnings_stderr_none.patch looks good to me. It can be applied on Python 2.7, 3.4 and 3.5.

[python-dev]

New changeset d04dab84388f by Serhiy Storchaka in branch '3.4':
Issue bpo-23016: A warning no longer produces AttributeError when the program
https://hg.python.org/cpython/rev/d04dab84388f

New changeset 0050e770b34c by Serhiy Storchaka in branch 'default':
Issue bpo-23016: A warning no longer produces an AttributeError when the program
https://hg.python.org/cpython/rev/0050e770b34c

New changeset aeeec8a4b9b8 by Serhiy Storchaka in branch '2.7':
Issue bpo-23016: A warning no longer produces an AttributeError when sys.stderr
https://hg.python.org/cpython/rev/aeeec8a4b9b8

[Arfrever]

•        # sys.stderr is None when ran with pythonw.exe - warnings get lost
  

s/ran/run/