Incorrect behavior of inspect.signature(f).bind

[slavkostrov]

BPO	42940

^{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 = None
created_at = <Date 2021-01-16.16:30:52.922>
labels = ['type-bug', '3.8', '3.9']
title = 'Incorrect behavior of inspect.signature(f).bind'
updated_at = <Date 2021-01-16.16:30:52.922>
user = 'https://bugs.python.org/slavkostrov'

bugs.python.org fields:

activity = <Date 2021-01-16.16:30:52.922>
actor = 'slavkostrov'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2021-01-16.16:30:52.922>
creator = 'slavkostrov'
dependencies = []
files = []
hgrepos = []
issue_num = 42940
keywords = []
message_count = 1.0
messages = ['385143']
nosy_count = 1.0
nosy_names = ['slavkostrov']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue42940'
versions = ['Python 3.8', 'Python 3.9']

Linked PRs

• gh-87106: Fix inspect.signature.bind handling of positional-only arguments with **kwargs #103404
• [3.12] gh-87106: Fix inspect.signature.bind() handling of positional-only arguments with **kwargs (GH-103404) #118984
• [3.13] gh-87106: Fix inspect.signature.bind() handling of positional-only arguments with **kwargs (GH-103404) #118985

[slavkostrov]

>>> def foo(a, /, b=1, **kwargs): pass
...
>>> foo(a=1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: foo() missing 1 required positional argument: 'a'

>>> inspect.signature(foo).bind(a=1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "\Python\Python39\lib\inspect.py", line 3062, in bind
    return self._bind(args, kwargs)
  File "\Python\Python39\lib\inspect.py", line 2958, in _bind
    raise TypeError(msg) from None
TypeError: 'a' parameter is positional only, but was passed as a keyword

There is a different behaviour between a simple function call and inspect.signature(foo).bind - different TypeError messages.

I think inspect should check for VARKEYWORDS before throwing an error and throw only if there are not.

[jacobtylerwalls]

In another case, inspect.signature(foo).bind gives a TypeError when no TypeError is even raised in the actual call:

>>> def foo(a=0, /, b=1, **kwargs): pass
...
>>> foo(a=1)
>>> inspect.signature(foo).bind(a=1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/inspect.py", line 3037, in bind
    return self._bind(args, kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/inspect.py", line 2933, in _bind
    raise TypeError(msg) from None
TypeError: 'a' parameter is positional only, but was passed as a keyword