inspect.getcallargs raises TypeError on valid arguments

[durban]

BPO	11256
Nosy	@benjaminp, @Trundle, @durban
Files	issue11256.diff: Patch (py3k branch) issue11256_2.diff: Patch with more tests issue11256_py27.patch issue11256_3.diff: New patch with corrected fix and more tests issue11256_4.patch: Patch for the new mercurial repository

^{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 2011-03-28.22:41:06.233>
created_at = <Date 2011-02-20.12:11:08.725>
labels = ['type-bug', 'library']
title = 'inspect.getcallargs raises TypeError on valid arguments'
updated_at = <Date 2011-03-28.22:41:06.231>
user = 'https://github.com/durban'

bugs.python.org fields:

activity = <Date 2011-03-28.22:41:06.231>
actor = 'python-dev'
assignee = 'none'
closed = True
closed_date = <Date 2011-03-28.22:41:06.233>
closer = 'python-dev'
components = ['Library (Lib)']
creation = <Date 2011-02-20.12:11:08.725>
creator = 'daniel.urban'
dependencies = []
files = ['20805', '20911', '20927', '20930', '21281']
hgrepos = []
issue_num = 11256
keywords = ['patch']
message_count = 7.0
messages = ['128902', '128907', '129538', '129608', '129620', '131340', '132439']
nosy_count = 5.0
nosy_names = ['gsakkis', 'benjamin.peterson', 'Trundle', 'daniel.urban', 'python-dev']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue11256'
versions = ['Python 2.7', 'Python 3.2', 'Python 3.3']

[durban]

inspect.getcallargs raises TypeError if given a function with only **kwargs, and some keyword arguments:

Python 3.3a0 (py3k:88451, Feb 20 2011, 12:37:22) 
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 
>>> from inspect import getcallargs
>>> 
>>> def f(**kwargs): pass
... 
>>> f(a=1, b=2)
>>> 
>>> getcallargs(f, a=1, b=2)
Traceback (most recent call last):
    ...
TypeError: f() takes no arguments (2 given)

In line 946 of inspect.py the "num_args == 0 and num_total" condition is true: the function expects 0 positional arguments and got more than zero arguments, but in this case these are keyword arguments, so it shouldn't raise TypeError.

[durban]

Here is a patch. It also includes tests that would have detected this bug. It also corrects a case when getcallargs raised an exception with a different message (there are tests also for this):

>>> def f(**kwargs): pass
... 
>>> f(1, a=2)
Traceback (most recent call last):
    ...
TypeError: f() takes exactly 0 positional arguments (2 given)
>>> 
>>> getcallargs(f, 1, a=2)
Traceback (most recent call last):
    ...
TypeError: f() takes no arguments (2 given)

There is a comment in the patch about this case: the message given by Python is also incorrect, because it says that 2 positional arguments are given, but there was only 1 positional argument (the other was a keyword argument). The patch currently handles this case by producing the same (incorrect) message as Python.

[durban]

Updated patch with extra tests.

[Trundle]

Confirmed under Python 2.7, 3.2 and 3.3. Patch looks good to me. Attached is a patch for 2.7.

[durban]

I found another case, when this is a problem: if there are no **kwargs, but there are some keyword-only arguments:

>>> def f(*, a, b): pass
... 
>>> f(a=1, b=2)
>>> 
>>> getcallargs(f, a=1, b=2)
Traceback (most recent call last):
    ...
TypeError: f() takes no arguments (2 given)

The attached issue11256_3.diff patch also fixes this problem, and adds tests that would have detected this case.

[durban]

Updated the patch for mercurial.

[python-dev]

New changeset 57e99f5f5e8f by Benjamin Peterson in branch '3.2':
Correct handling of functions with only kwarg args in getcallargs (closes bpo-11256)
http://hg.python.org/cpython/rev/57e99f5f5e8f

New changeset b19d76d9d2a7 by Benjamin Peterson in branch '2.7':
Correct handling of functions with only kwarg args in getcallargs (closes bpo-11256)
http://hg.python.org/cpython/rev/b19d76d9d2a7