Strange behavior argparse.BooleanOptionalAction

[tomazfs]

Bug report

Bug description:

In [1]: import argparse
   ...: parser = argparse.ArgumentParser()
   ...: parser.add_argument('--foobar', action=argparse.BooleanOptionalAction)
   ...: parser.add_argument('--foo', action="store_true")
   ...: parser.parse_args(['--no-foo'])
Out[1]: Namespace(foobar=False, foo=False)

In [2]: parser = argparse.ArgumentParser()
   ...: parser.add_argument('--foo-bar', action=argparse.BooleanOptionalAction)
   ...: parser.add_argument('--foo', action="store_true")
   ...: parser.parse_args(['--no-foo'])
Out[2]: Namespace(foo_bar=False, foo=False)

Is this expected? There is no '--no-foo' option, but using it sets '--foobar', '--foo-bar' and '--foo' to False. I have tested this on Python 3.12.10 and Python 3.13.3.

CPython versions tested on:

3.13

Operating systems tested on:

Windows

[serhiy-storchaka]

But there is '--no-foobar' or '--no-foo-bar' option. '--no-foo' is just an abbreviation of it. You can disable option abbreviation by passing allow_abbrev=False to the ArgumentParser constructor.

[StanFromIreland]

This should be closed, Serhiy already provided an explanation for the user error.

[donBarbos]

Already answered, but I'll add that there was a similar problem recently: #131175