argparse note

A note about argparse, the Python command line parsing tool

reference

Manual, Tutorial

Typical use case

import argparse

def main():
    parser = argparse.ArgumentParser(
        formatter_class=argparse.RawDescriptionHelpFormatter,
        description="Concatenates a person's files",
        epilog='''Notices:
    1. You need an account first.
    2. Files should exist.
'''
    )
    parser.add_argument(
        '-o', '--outfile', default='foo.txt', help='Output file name')
    parser.add_argument(
        '-q', '--quiet', action='store_true', dest='qFlag',
        help='No messages to console')
    parser.add_argument(
        '-r', '--repeat', type=int, default=1, help='Repeat count')
    parser.add_argument(
        '-m', '--mode', required=True, choices=['t', 'b'], help='Mode')
    parser.add_argument('person', help='Person name')
        # mandatory positional argument
    parser.add_argument('infile', nargs='*', help='Input file name')
        # '+' can also be used for nargs
    group = parser.add_mutually_exclusive_group(required=True)
    group.add_argument('--private', action='store_true')
    group.add_argument('--public',  action='store_true')
    args = parser.parse_args()

    print(f'outfile = {args.outfile}')            # long name is prefered
    print(f'quiet = {args.qFlag}')                # dest='qFlag'
    print(f'repeat count = {args.repeat * 100}')  # type=int
    print(f'# of infiles = {len(args.infile)}')   # stored as a list

main()

Execution example

$ ./a.py -m t --private uid a b c
outfile = foo.txt
quiet = False
repeat count = 100
# of infiles = 3

point

• Items starting with a hyphen are optional. If not, the position parameter
• When using, access with ʻargs. Name`.
• Priority is given to names with two or more characters.
• It can also be specified by dest.
• The default value of the option is default = value
• True / False flag is ʻaction ='store_true'`
• If type = int, it becomes an integer.
• Optional option is required = True
• Selection from the specified is choices = list
• Multiple specifications are nargs ='*' and nargs ='+'
• Options that cannot be specified at the same time are created with ʻadd_mutually_exclusive_group`.
• description is padded with blanks and line breaks, but this is not the case if you specify formatter_argparse.RawDescriptionHelpFormatter.