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Support of mutually exclusive groups in the argparse help is very limited #142346
Description
Bug report
argparse supports grouping mutually exclusive arguments in the usage. For example:
import argparse
parser = argparse.ArgumentParser(prog="PROG")
group = parser.add_mutually_exclusive_group()
group.add_argument('-f', action='store_true')
group.add_argument('x', nargs='?')
print(parser.format_usage())Output:
usage: PROG [-h] [-f | x]
But it does not work if there is a positional argument before a mutually exclusive group containing positional argument:
import argparse
parser = argparse.ArgumentParser(prog="PROG")
parser.add_argument('x')
group = parser.add_mutually_exclusive_group()
group.add_argument('-f', action='store_true')
group.add_argument('y', nargs='?')
print(parser.format_usage())Output:
usage: PROG [-h] [-f] x [y]
Expected output:
usage: PROG [-h] x [-f | y]
Or there is an optional argument after a mutually exclusive group:
import argparse
parser = argparse.ArgumentParser(prog="PROG")
group = parser.add_mutually_exclusive_group()
group.add_argument('-f', action='store_true')
group.add_argument('x', nargs='?')
parser.add_argument('-g', action='store_true')
print(parser.format_usage())Output:
usage: PROG [-h] [-f] [-g] [x]
Expected output:
usage: PROG [-h] [-f | x] [-g]
Or there are multiple mutually exclusive groups:
import argparse
parser = argparse.ArgumentParser(prog="PROG")
group1 = parser.add_mutually_exclusive_group()
group1.add_argument('-f', action='store_true')
group1.add_argument('x', nargs='?')
group2 = parser.add_mutually_exclusive_group()
group2.add_argument('-g', action='store_true')
group2.add_argument('y', nargs='?')
print(parser.format_usage())Output:
usage: PROG [-h] [-f] [-g] [x] [y]
Expected output:
usage: PROG [-h] [-f | x] [-g | y]
(or something like).
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pythongh-142346: Fix usage formatting for mutually exclusive groups i…
gh-142346: Fix usage formatting for mutually exclusive groups in argp…
pythongh-142346: Fix usage formatting for mutually exclusive groups i…
[3.14] gh-142346: Fix usage formatting for mutually exclusive groups …
serhiy-storchaka commentedon Dec 8, 2025
It cannot be backported to 3.13 because the new algorithm does not work with nested mutually exclusive groups, which were deprecated and removed in 3.14.