Custom usage message for many-valued argument

Question

Given sth. like (or similar to):

import argparse
parser = argparse.ArgumentParser()
parser.add_argument("FILES", nargs="+", type=str)
args = parser.parse_args()

Now I'd like to have the many-valued positional argument FILES displayed in the usage message as

usage: cli.py [-h] FILES

instead of

usage: cli.py [-h] FILES [FILES ...]

Any step-by-step explanations or pointers are appreciated.

Answer 1

This is the built-in behavior of the default formatter: source.

You could have your custom formatter with special handling for the nargs="+" type arguments:

import argparse


class CustomFormatter(argparse.HelpFormatter):
    def _format_args(self, action, default_metavar):
        get_metavar = self._metavar_formatter(action, default_metavar)
        if action.nargs == argparse.ONE_OR_MORE:
            return '%s' % get_metavar(1)
        else:
            return super(CustomFormatter, self)._format_args(action, default_metavar)


parser = argparse.ArgumentParser(formatter_class=CustomFormatter)
parser.add_argument("FILES", nargs="+", type=str)
args = parser.parse_args()

Would print out:

usage: cli.py [-h] FILES
cli.py: error: the following arguments are required: FILES