inspect.signature.bind does not correctly handle keyword argument with same name as positional-only parameter

[orez]

BPO	38478
Nosy	@pablogsal, @miss-islington, @orez-
PRs	bpo-38478: Correctly handle keyword argument with same name as positional-only parameter #16800 [3.8] bpo-38478: Correctly handle keyword argument with same name as positional-only parameter (GH-16800) #16801

^{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/pablogsal'
closed_at = <Date 2019-10-15.12:46:36.956>
created_at = <Date 2019-10-15.02:26:32.669>
labels = ['3.8', 'type-bug', 'library', '3.9']
title = 'inspect.signature.bind does not correctly handle keyword argument with same name as positional-only parameter'
updated_at = <Date 2019-10-15.12:46:36.955>
user = 'https://github.com/orez'

bugs.python.org fields:

activity = <Date 2019-10-15.12:46:36.955>
actor = 'pablogsal'
assignee = 'pablogsal'
closed = True
closed_date = <Date 2019-10-15.12:46:36.956>
closer = 'pablogsal'
components = ['Library (Lib)']
creation = <Date 2019-10-15.02:26:32.669>
creator = 'brian.shaginaw'
dependencies = []
files = []
hgrepos = []
issue_num = 38478
keywords = ['patch']
message_count = 4.0
messages = ['354683', '354710', '354714', '354718']
nosy_count = 3.0
nosy_names = ['pablogsal', 'miss-islington', 'brian.shaginaw']
pr_nums = ['16800', '16801']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue38478'
versions = ['Python 3.8', 'Python 3.9']

[orez]

>>> import inspect
>>> def foo(bar, /, **kwargs):
...   print(bar, kwargs)
...
>>> foo(1, bar=2)
1 {'bar': 2}
>>> inspect.signature(foo).bind(1, bar=2)
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 3025, in bind
    return self._bind(args, kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/inspect.py", line 2964, in _bind
    raise TypeError(
TypeError: multiple values for argument 'bar'

Python 3.8 introduced positional-only parameters, which allow parameter names to remain available for use in **kwargs. It looks like inspect.signature.bind does not recognize this, and thinks the parameter is being passed twice, which causes the above TypeError.

Expected result: <BoundArguments (bar=1, kwargs={'bar': 2})>

[pablogsal]

Thanks, Brian for the report!

I have a fix ready. When merged, this will be available in the next release.

[pablogsal]

New changeset f3ef06a by Pablo Galindo in branch 'master':
bpo-38478: Correctly handle keyword argument with same name as positional-only parameter (GH-16800)
f3ef06a

[miss-islington]

New changeset f705f8e by Miss Islington (bot) in branch '3.8':
bpo-38478: Correctly handle keyword argument with same name as positional-only parameter (GH-16800)
f705f8e