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PyArg_ParseTupleAndKeywords doesn't take const char *keywords[] #65210

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hvenev mannequin opened this issue Mar 21, 2014 · 5 comments
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PyArg_ParseTupleAndKeywords doesn't take const char *keywords[] #65210

hvenev mannequin opened this issue Mar 21, 2014 · 5 comments
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topic-C-API type-feature A feature request or enhancement

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@hvenev
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hvenev mannequin commented Mar 21, 2014 •
edited by bedevere-bot
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BPO 21011
Nosy @methane, @serhiy-storchaka, @MojoVampire, @hvenev

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 2014-03-21.16:45:16.140>
labels = ['extension-modules', 'type-feature', '3.8']
title = "PyArg_ParseTupleAndKeywords doesn't take const char *keywords[]"
updated_at = <Date 2018-07-03.09:45:24.075>
user = 'https://github.com/hvenev'

bugs.python.org fields:

activity = <Date 2018-07-03.09:45:24.075>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Extension Modules']
creation = <Date 2014-03-21.16:45:16.140>
creator = 'h.venev'
dependencies = []
files = []
hgrepos = []
issue_num = 21011
keywords = []
message_count = 4.0
messages = ['214388', '214857', '320945', '320952']
nosy_count = 4.0
nosy_names = ['methane', 'serhiy.storchaka', 'josh.r', 'h.venev']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue21011'
versions = ['Python 3.8']

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@hvenev
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hvenev mannequin commented Mar 21, 2014

This really annoys me. I have to store the literals in char[] and then make a char*[] from them. It would be better if a simple array of string literals could be used. It would also require less data space because string literals could be merged by the compiler.

I don't know why PyArg_ParseTupleAndKeywords would ever modify the keywords array so it makes absolutely no sense to me for the array not to be const char*[].

In all cases I have seen PyArg_ParseTupleAndKeywords being used string literals were converted to char* (dropping const) which is far far worse than inefficient code.

@hvenev hvenev mannequin added performance Performance or resource usage extension-modules C modules in the Modules dir labels Mar 21, 2014
@MojoVampire
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MojoVampire mannequin commented Mar 25, 2014

This has come up before. Links to additional info:

https://mail.python.org/pipermail/python-dev/2006-February/060689.html

http://bugs.python.org/issue1772673

@methane
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methane commented Jul 3, 2018

I think we can't fix this until Python 4.
May I close this issue as "won't fix" for now?

Or can we add "Python 4" keyword to list backward incompatible changes we want to do in the future?

@methane methane added the 3.8 (EOL) end of life label Jul 3, 2018
@serhiy-storchaka
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We can't change this API because this would break virtually all user code.

But we can introduce a macro like PY_SSIZE_T_CLEAN. If it is defined before including Python.h, PyArg_ParseTupleAndKeywords() will take an array of const strings. This will help for compatibility with C++.

@serhiy-storchaka serhiy-storchaka added type-feature A feature request or enhancement and removed performance Performance or resource usage labels Jul 3, 2018
@ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
@iritkatriel iritkatriel added topic-C-API and removed extension-modules C modules in the Modules dir 3.8 (EOL) end of life labels May 14, 2023
@iritkatriel iritkatriel mentioned this issue May 14, 2023
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@bedevere-bot bedevere-bot mentioned this issue Jun 21, 2023
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serhiy-storchaka added a commit to serhiy-storchaka/cpython that referenced this issue Jun 21, 2023
@serhiy-storchaka
pythongh-65210: Add const qualifiers in PyArg_VaParseTupleAndKeywords()
80e37a9 
Change the declaration of the keywords parameter in functions
PyArg_ParseTupleAndKeywords() and PyArg_VaParseTupleAndKeywords() from `char **`
to `char * const *` in C and `const char * const *` in C++.

It makes these functions compatible with argument of type `const char * const *`,
`const char **` or `char * const *` in C++ and `char * const *` in C
without explicit type cast.
@serhiy-storchaka
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We can fix this at least for C++, because in C++ the const char * const * declaration is compatible with arguments of type const char * const *, char * const *, const char **, and char **.

Sad, it is not so in C, but we can provide a lever to control the declaration, and may change the default in distant future.

serhiy-storchaka added a commit that referenced this issue Dec 4, 2023
@serhiy-storchaka @CAM-Gerlach
gh-65210: Add const qualifiers in PyArg_VaParseTupleAndKeywords() (GH…
da6760b 
…-105958)

Change the declaration of the keywords parameter in functions
PyArg_ParseTupleAndKeywords() and PyArg_VaParseTupleAndKeywords() from `char **`
to `char * const *` in C and `const char * const *` in C++.

It makes these functions compatible with argument of type `const char * const *`,
`const char **` or `char * const *` in C++ and `char * const *` in C
without explicit type cast.

Co-authored-by: C.A.M. Gerlach <[email protected]>
aisk pushed a commit to aisk/cpython that referenced this issue Feb 11, 2024
@serhiy-storchaka @CAM-Gerlach @aisk
pythongh-65210: Add const qualifiers in PyArg_VaParseTupleAndKeywords…
4fb94c8 
…() (pythonGH-105958)

Change the declaration of the keywords parameter in functions
PyArg_ParseTupleAndKeywords() and PyArg_VaParseTupleAndKeywords() from `char **`
to `char * const *` in C and `const char * const *` in C++.

It makes these functions compatible with argument of type `const char * const *`,
`const char **` or `char * const *` in C++ and `char * const *` in C
without explicit type cast.

Co-authored-by: C.A.M. Gerlach <[email protected]>
Glyphack pushed a commit to Glyphack/cpython that referenced this issue Sep 2, 2024
@serhiy-storchaka @CAM-Gerlach @Glyphack
pythongh-65210: Add const qualifiers in PyArg_VaParseTupleAndKeywords…
a01a009 
…() (pythonGH-105958)

Change the declaration of the keywords parameter in functions
PyArg_ParseTupleAndKeywords() and PyArg_VaParseTupleAndKeywords() from `char **`
to `char * const *` in C and `const char * const *` in C++.

It makes these functions compatible with argument of type `const char * const *`,
`const char **` or `char * const *` in C++ and `char * const *` in C
without explicit type cast.

Co-authored-by: C.A.M. Gerlach <[email protected]>
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