Does argparse (python) support mutually exclusive groups of arguments?

Question

If I have the arguments \'-a\', \'-b\', \'-c\', \'-d\', with the add_mutually_exclusive_group() function my program will have to use just one of th

Answer 1

The argparse enhancement request referenced in @hpaulj's comment is still open after more than nine years, so I figured other people might benefit from the workaround I just discovered. Based on this comment in the enhancement request, I found I was able to add an option to two different mutually-exclusive groups using this syntax:

#!/usr/bin/env python                                                                                                                                                                     
import argparse
import os
import sys

def parse_args():
    parser = argparse.ArgumentParser(
        formatter_class=argparse.ArgumentDefaultsHelpFormatter
    )

    parser.add_argument("-d", "--device", help="Path to UART device", default="./ttyS0")

    mutex_group1 = parser.add_mutually_exclusive_group()
    mutex_group2 = parser.add_mutually_exclusive_group()

    mutex_group1.add_argument(
        "-o",
        "--output-file",
        help="Name of output CSV file",
        default="sensor_data_sent.csv",
    )

    input_file_action = mutex_group1.add_argument(
        "-i", "--input-file", type=argparse.FileType("r"), help="Name of input CSV file"
    )

    # See: https://bugs.python.org/issue10984#msg219660
    mutex_group2._group_actions.append(input_file_action)

    mutex_group2.add_argument(
        "-t",
        "--time",
        type=int,
        help="How long to run, in seconds (-1 = loop forever)",
        default=-1,
    )

    # Add missing ']' to usage message
    usage = parser.format_usage()
    usage = usage.replace('usage: ', '')
    usage = usage.replace(']\n', ']]\n')
    parser.usage = usage

    return parser.parse_args()


if __name__ == "__main__":
    args = parse_args()
    print("Args parsed successfully...")
    sys.exit(0)

This works well enough for my purposes:

$ ./fake_sensor.py -i input.csv -o output.csv                                                                                                                                             
usage: fake_sensor.py [-h] [-d DEVICE] [-o OUTPUT_FILE | [-i INPUT_FILE | -t TIME]]
fake_sensor.py: error: argument -o/--output-file: not allowed with argument -i/--input-file

$ ./fake_sensor.py -i input.csv -t 30         
usage: fake_sensor.py [-h] [-d DEVICE] [-o OUTPUT_FILE | [-i INPUT_FILE | -t TIME]]
fake_sensor.py: error: argument -t/--time: not allowed with argument -i/--input-file

$ ./fake_sensor.py -i input.csv
Args parsed successfully...

$ ./fake_sensor.py -o output.csv
Args parsed successfully...

$ ./fake_sensor.py -o output.csv -t 30
Args parsed successfully...

Accessing private members of argparse is, of course, rather brittle, so I probably wouldn't use this approach in production code. Also, an astute reader may notice that the usage message is misleading, since it implies that -o and -i can be used together when they cannot(!) However, I'm using this script for testing only, so I'm not overly concerned. (Fixing the usage message 'for real' would, I think, require much more time than I can spare for this task, but please comment if you know a clever hack for this.)