Signal module doesnt raises ValueError Exception

[rsevcan]

BPO	21382
Nosy	@tjguk, @briancurtin, @florentx, @berkerpeksag

^{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 2016-04-23.23:59:58.665>
created_at = <Date 2014-04-29.08:17:16.354>
labels = ['type-bug', 'OS-windows', 'docs']
title = 'Signal module doesnt raises ValueError Exception'
updated_at = <Date 2016-04-23.23:59:58.663>
user = 'https://bugs.python.org/rsevcan'

bugs.python.org fields:

activity = <Date 2016-04-23.23:59:58.663>
actor = 'berker.peksag'
assignee = 'docs@python'
closed = True
closed_date = <Date 2016-04-23.23:59:58.665>
closer = 'berker.peksag'
components = ['Documentation', 'Windows']
creation = <Date 2014-04-29.08:17:16.354>
creator = 'rsevcan'
dependencies = []
files = []
hgrepos = []
issue_num = 21382
keywords = []
message_count = 4.0
messages = ['217486', '217531', '217996', '264077']
nosy_count = 7.0
nosy_names = ['tim.golden', 'brian.curtin', 'flox', 'docs@python', 'python-dev', 'berker.peksag', 'rsevcan']
pr_nums = []
priority = 'low'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue21382'
versions = ['Python 2.7', 'Python 3.5', 'Python 3.6']

[rsevcan]

signal.signal() built-in function doesnt throws a ValueError exception in Windows when is called with a different signal than SIGABRT, SIGFPE, SIGILL, SIGINT, SIGSEGV, or SIGTERM, as it is written in the documentation.

https://docs.python.org/2/library/signal.html#signal.signal
https://docs.python.org/3/library/signal.html#signal.signal

It throws an AttributeError Exception

>>> import signal
>>> import sys
>>> sys.platform
'win32'
>>> signal.signal(signal.SIGPIPE, lambda signum, frame: sys.exit(1))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'SIGPIPE'
>>>

Regards

[florentx]

It's about documentation only.

The sentence is not wrong, but it is slightly confusing, and there's no hint which signals are defined on Windows.

"On Windows, signal() can only be called with SIGABRT, SIGFPE, SIGILL, SIGINT, SIGSEGV, or SIGTERM. A ValueError will be raised in any other case."

Reading only this documentation, if the developer doesn't have a test platform on Windows, he could blindly write:

try:
signal.signal(signal.SIGPIPE, lambda signum, frame: sys.exit(1))
except ValueError:
pass

... until a Windows user detects the issue (thank you rsevcan)

Now I just found this page which is relevant here ... either we could link to the page in a "See also" section, or give an hint about which signals are defined or not.
http://msdn.microsoft.com/en-us/library/xdkz3x12.aspx

[tjguk]

To be honest I can't get excited about this one. The only sensible change is to remove the rather specific comment about ValueError and just leave the fact that only certain signals are valid.

Because the C code defines module-level constants on the basis of whether the platform C-lib defines them, different platforms will have different module attributes. It would be unusual for us to list all the combinations.

Adding Brian Curtin as he made the original change.

[python-dev]

New changeset 1fcf68e6f4c7 by Berker Peksag in branch '3.5':
Issue bpo-21382: Clarify signal.signal() documentation on Windows
https://hg.python.org/cpython/rev/1fcf68e6f4c7

New changeset 3e27b21e3a7d by Berker Peksag in branch 'default':
Issue bpo-21382: Clarify signal.signal() documentation on Windows
https://hg.python.org/cpython/rev/3e27b21e3a7d