PyArg_ParseTupleAndKeywords doesn't take const char *keywords[]

@methane

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']

Linked PRs

gh-65210: Add const qualifiers in PyArg_VaParseTupleAndKeywords() #105958

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.

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

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?

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++.

pythongh-65210: Add const qualifiers in PyArg_VaParseTupleAndKeywords()

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.

gh-65210: Add const qualifiers in PyArg_VaParseTupleAndKeywords() (GH…

pythongh-65210: Add const qualifiers in PyArg_VaParseTupleAndKeywords…

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

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

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hvenev commented on Mar 21, 2014

MojoVampire commented on Mar 25, 2014

methane commented on Jul 3, 2018

serhiy-storchaka commented on Jul 3, 2018

serhiy-storchaka commented on Jun 21, 2023

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