New submission from Phil Elson:
When passing an invalid Warning subclasses to the warnings.warn function, a
bare issubclass exception is raised:
>>> import warnings
>>> warnings.warn('hello world', 'not a valid warning type')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: issubclass() arg 1 must be a class
This exception is consistent accross both Python/_warnings.c and
Lib/warnings.py implementations, but I feel it could be more helpful/explicit
about the nature problem.
To test both cases I have been using the following code (python3.4):
>>> import test.support
>>> py_warnings = test.warnings = test.support.import_fresh_module('warnings',
>>> blocked=['_warnings'])
>>> c_warnings = test.support.import_fresh_module('warnings',
>>> fresh=['_warnings'])
Now:
>>> py_warnings.warn('hello world', '')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "lib/python3.4/warnings.py", line 168, in warn
assert issubclass(category, Warning)
TypeError: issubclass() arg 1 must be a class
>>> c_warnings.warn('hello world', '')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: issubclass() arg 1 must be a class
Additionally, there is a difference in the denotational semantics of None
between the c and py warnings implementation:
>>> py_warnings.warn('Hello world', None)
__main__:1: UserWarning: Hello world
>>> c_warnings.warn('Hello world', None)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: issubclass() arg 1 must be a class
I can understand that python does not allow the concept of an optional
positional arguments and therefore it is arguable that the signatures of the
two functions are inevitably going to be different. I defer to someone more
knowledgeable in Python to decide if this is a problem, and whether it should
be made consistent.
Attached is a patch to address these two issues, with associated tests. Please
review (n.b. I am a python developer at heart, and only dabble in C when I have
to, so extra scrutiny on the C would be valuable to me) and I'd be happy to get
any necessary changed applied to the patch asap.
In short, as a result of applying this patch, the following results ensue:
>>> py_warnings.warn('hello world', '')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "lib/python3.4/warnings.py", line 175, in warn
'Got {!r}'.format(Warning, category)) from None
ValueError: category must be a subclass of <class 'Warning'>.Got ''
>>> c_warnings.warn('hello world', '')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: category must be a subclass of <class 'Warning'>. Got ''.
>>>
>>> c_warnings.warn('hello world', None)
__main__:1: UserWarning: hello world
Thanks!
----------
components: Library (Lib)
files: pelson_warnings_fix.diff
keywords: patch
messages: 174421
nosy: pelson
priority: normal
severity: normal
status: open
title: Better warnings exception for bad category
type: behavior
versions: Python 3.4
Added file: http://bugs.python.org/file27824/pelson_warnings_fix.diff
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue16382>
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