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Incorrect interaction between argparse nargs='*' and choices #92445

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@rhettinger

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@rhettinger

In the code below, it is valid to supply no arguments.

from argparse import ArgumentParser

p = ArgumentParser()
p.add_argument('dessert', nargs='*', choices=('cake', 'pie'))
p.parse_args([])

However, the following error is generated:

usage: tmp5.py [-h] [{cake,pie} ...]
tmp5.py: error: argument dessert: invalid choice: [] (choose from 'cake', 'pie')

What is happening is that the empty list is being treated a value rather than a collection of values.

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    3.10only security fixes3.11only security fixes3.12only security fixes3.9only security fixeseasystdlibPython modules in the Lib dirtype-bugAn unexpected behavior, bug, or error

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