Easy way to deprecate arguments with argparse

deprecate_args.py

import argparse
import warnings


class DeprecateAction(argparse.Action):
    def __call__(self, parser, namespace, values, option_string=None):
        warnings.warn("Argument %s is deprecated and is *ignored*." % self.option_strings)
        delattr(namespace, self.dest)


parser = argparse.ArgumentParser()

parser.add_argument("-f", "--foo", action="store_true")
parser.add_argument("-b", "--bar", type=int, action=DeprecateAction, help="just a good old int")
parser.add_argument("-c", "--choo")


def mark_deprecated_help_strings(parser, prefix="DEPRECATED"):
    for action in parser._actions:
        if isinstance(action, DeprecateAction):
            h = action.help
            if h is None:
                action.help = prefix
            else:
                action.help = prefix + ": " + h

mark_deprecated_help_strings(parser)
args = parser.parse_args()
print(args)  # Namespace(x=y, ...)

Super useful! But to anyone else looking to deprecate arguments, deprecate=True is supported in argparse from Python v3.12+.