[New-bugs-announce] [issue42457] ArgumentParser nested subparsers resolve paths in improper order

[Carson Wilber]

New submission from Carson Wilber <carsonwilber at gmail.com>:

ArgumentParser improperly resolves arguments in an improper order when using nested subparsers if there are required arguments at more than one layer.

A minimum viable reproduction is to create a set of subparsers on a primary parser, and a set of subparsers on at least one of those parsers. On the main parser and the first-level subparser, add a required argument (in any position as they are appended to the end.)

If you attempt to, for example, print the help for a second-level subparser, an error will be thrown and the parser will exit due to the required argument(s) not being provided, despite the expected behavior and the nature of the -h flag not requiring those arguments to be provided.

For lack of an appropriate means to show a complete minimum viable reproduction here, please see this StackOverflow thread I initially created believing this to be user error (having now determined this is a bug in behavior):

https://stackoverflow.com/questions/64908447/printing-help-for-nested-subparsers-with-required-positional-arguments

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messages: 381789
nosy: carsonwilber
priority: normal
severity: normal
status: open
title: ArgumentParser nested subparsers resolve paths in improper order
type: behavior
versions: Python 3.10, Python 3.6, Python 3.7, Python 3.8, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue42457>
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