gh-77956: Add the words 'default' and 'version' help text localizable

[eamanu]

bpo-33775: argparse: the word 'default' (in help) is not marked as translatable

and bpo-16786: argparse doesn't offer localization interface for "version" action

Co-authored-by: paul.j3

• Issue: argparse: the word 'default' (in help) is not marked as translatable #77956

[tirkarthi]

This needs tests and I am not sure how to test this since argparse lacks localization tests. As noted by paul.j3 I am not sure how worthy enough it is to make this change that doesn't have tests and something the user can override by having a custom help formatter.

Wrapping the whole help string at https://github.com/python/cpython/pull/12711/files#diff-837b312b1f3508216ace6adb46492836R682 will cause %(default)s also to be changed as a translated variable name causing KeyError. I think the issue was to just make word default in help translatable.

Sample program where I directly patch gettext so that translation just gives uppercase of the word :

import gettext

def my_gettext(s):
    return s.upper()

gettext.gettext = my_gettext

import argparse

if __name__ == "__main__":
    parser = argparse.ArgumentParser(formatter_class=argparse.ArgumentDefaultsHelpFormatter)
    parser.add_argument("-a", default=1, help= "Test help")
    args = parser.parse_args()

python3 ../backups/bpo33775.py --help
USAGE: bpo33775.py [-h] [-a A]

OPTIONAL ARGUMENTS:
  -h, --help  SHOW THIS HELP MESSAGE AND EXIT
  -a A        Test help (default: 1)

with patch %(default)s is changed to %(DEFAULT)s:

./python.exe ../backups/bpo33775.py --help
Traceback (most recent call last):
  File "../backups/bpo33775.py", line 12, in <module>
    args = parser.parse_args()
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/argparse.py", line 1746, in parse_args
    args, argv = self.parse_known_args(args, namespace)
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/argparse.py", line 1778, in parse_known_args
    namespace, args = self._parse_known_args(args, namespace)
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/argparse.py", line 1984, in _parse_known_args
    start_index = consume_optional(start_index)
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/argparse.py", line 1924, in consume_optional
    take_action(action, args, option_string)
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/argparse.py", line 1852, in take_action
    action(self, namespace, argument_values, option_string)
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/argparse.py", line 1034, in __call__
    parser.print_help()
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/argparse.py", line 2471, in print_help
    self._print_message(self.format_help(), file)
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/argparse.py", line 2455, in format_help
    return formatter.format_help()
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/argparse.py", line 281, in format_help
    help = self._root_section.format_help()
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/argparse.py", line 212, in format_help
    item_help = join([func(*args) for func, args in self.items])
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/argparse.py", line 212, in <listcomp>
    item_help = join([func(*args) for func, args in self.items])
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/argparse.py", line 212, in format_help
    item_help = join([func(*args) for func, args in self.items])
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/argparse.py", line 212, in <listcomp>
    item_help = join([func(*args) for func, args in self.items])
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/argparse.py", line 522, in _format_action
    help_text = self._expand_help(action)
  File "/Users/karthikeyansingaravelan/stuff/python/cpython/Lib/argparse.py", line 611, in _expand_help
    return self._get_help_string(action) % params
KeyError: 'DEFAULT'

[jdetrey]

Dear all,

My two cents about this issue, as I would also like to see this PR merged :)

Wrapping the whole help string at https://github.com/python/cpython/pull/12711/files#diff-837b312b1f3508216ace6adb46492836R682 will cause %(default)s also to be changed as a translated variable name causing KeyError. I think the issue was to just make word default in help translatable.

I disagree with this comment: gettext translations should never change named arguments in format strings. Named arguments are actually recommended in the GNU gettext documentation (see the note at the end of the Python section).

Therefore, passing the whole string to _() (as done by this PR) is the way to go. It is also consistent with other calls to _() in the argparse module (see e.g. Lib/argparse.py:2212).

Kind regards,
Jérémie.

[arhadthedev]

@tirkarthi argparse already has a bunch of untested translatable strings so the PR is not a pioneer here:

cpython/Lib/argparse.py

Line 299 in 0097c36

prefix = _('usage: ')

cpython/Lib/argparse.py

Line 776 in 0097c36

format = _('argument %(argument_name)s: %(message)s')

cpython/Lib/argparse.py

Line 882 in 0097c36

raise NotImplementedError(_('.__call__() not defined'))

cpython/Lib/argparse.py

Line 1196 in 0097c36

self, _('conflicting subparser alias: %s') % alias)

cpython/Lib/argparse.py

Line 1231 in 0097c36

msg = _('unknown parser %(parser_name)r (choices: %(choices)s)') % args

and way more.

[m-aciek]

Looks good to me.

[serhiy-storchaka]

LGTM.

[serhiy-storchaka]

@tirkarthi, I agree with @jdetrey and @arhadthedev. Translation should not change %(default)s. Adding translation tests to argparse is a separate and more complex issue, this should not stop all bugfixes.

Stale review comment

[tirkarthi]

@serhiy-storchaka I have removed my request for changes since it was an old review. I can see argparse already has this approach as noted. Please go ahead with your review. Thanks.

[miss-islington-app]

Thanks @eamanu for the PR, and @serhiy-storchaka for merging it 🌮🎉.. I'm working now to backport this PR to: 3.11, 3.12.
🐍🍒⛏🤖

[miss-islington-app]

Sorry, @eamanu and @serhiy-storchaka, I could not cleanly backport this to 3.12 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker da382aaf52d761a037874bee27bb5db69906df9e 3.12

[miss-islington-app]

Sorry, @eamanu and @serhiy-storchaka, I could not cleanly backport this to 3.11 due to a conflict.
Please backport using cherry_picker on command line.

cherry_picker da382aaf52d761a037874bee27bb5db69906df9e 3.11

[bedevere-app]

GH-115967 is a backport of this pull request to the 3.12 branch.

[bedevere-app]

GH-115968 is a backport of this pull request to the 3.11 branch.