Python parser for command-line options, arguments and sub-commands (argparse)

The argparse module makes it easy to write user-friendly command-line interfaces.
Right after we are going to show basic examples of use of this parser.

• Let us start with a very simple example which does (almost) nothing:

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import argparse parser = argparse.ArgumentParser() parser.parse_args()

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$ ./argparse1.py -h usage: argparse1.py [-h] optional arguments: -h, --help show this help message and exit

Let us configure description, version and epilogue

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import argparse # prog = sys.argv[0], you could change if you want, prog="myprogram" parser = argparse.ArgumentParser(description='Description', version="%(prog)s 0.1", epilog="Epilogue") parser.parse_args()

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$ ./argparse2.py -h usage: argparse2.py [-h] [-v] Description optional arguments: -h, --help show this help message and exit -v, --version show program's version number and exit Epilogue

• Let us introduce a positional argument

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import argparse parser = argparse.ArgumentParser() parser.add_argument("argument") parser.parse_args()

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$ ./argparse3.py -h usage: argparse3.py [-h] argument positional arguments: argument Information about argument optional arguments: -h, --help show this help message and exit -v, --version show program's version number and exit Epilogue

• Let us introduce optional arguments

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import argparse parser = argparse.ArgumentParser() # A optional argument A with necessary value parser.add_argument("-a", "--argument-A", help="Information about argument with pattern [-a ARGUMENT]") # A optional argument B without necessary value parser.add_argument("-b", "--argument-B", help="Information about b argument with pattern [-b] ", action="store_true") parser.parse_args()

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$ ./argparse4.py -h usage: argparse4.py [-h] [-a ARGUMENT_A] [-b] optional arguments: -h, --help show this help message and exit -a ARGUMENT_A, --argument-A ARGUMENT_A Information about argument with pattern [-a ARGUMENT] -b, --argument-B Information about b argument with pattern [-b]

• Let us introduce subcommands

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import argparse parser = argparse.ArgumentParser() subparsers = parser.add_subparsers(help='sub-command help') # create the parser for the "a" command parser_a = subparsers.add_parser('a', help='a help') # create the parser for the "b" command parser_b = subparsers.add_parser('b', help='b help') parser.parse_args()

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$ ./argparse5.py -h usage: argparse5.py [-h] {a,b} ... positional arguments: {a,b} sub-command help a a help b b help optional arguments: -h, --help show this help message and exit

• Let us introduce mutual exclusion of arguments

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import argparse parser = argparse.ArgumentParser() group1 = parser.add_mutually_exclusive_group(required=True) group1.add_argument("-a", "--argument-A", action="store_true") group1.add_argument("-b", "--argument-B", action="store_false") group2 = parser.add_mutually_exclusive_group(required=True) group2.add_argument("-c", "--argument-C", help="c help") group2.add_argument("-d", "--argument-D", help="d help") parser.parse_args()

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$ ./argparse6.py -h usage: argparse6.py [-h] (-a | -b) (-c ARGUMENT_C | -d ARGUMENT_D) optional arguments: -h, --help show this help message and exit -a, --argument-A -b, --argument-B -c ARGUMENT_C, --argument-C ARGUMENT_C c help -d ARGUMENT_D, --argument-D ARGUMENT_D d help

• Finally, let us see how to execute action of optional argument, although positional argument is empt

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import sys import argparse # Parse the target url parser.add_argument ("url" , nargs='?', help="target URL") # Parse argument to show license parser.add_argument ("-l", "--license", help="show license", action="store_true") # Print license if args.license: print st.WS_LICENSE sys.exit(0)

The tricky is to use nargs='?' for positional argument and sys.exit(0)

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$ ./argparse7.py -h usage: argparse7.py [-l] [url] Description positional arguments: url target URL optional arguments: -h, --help show this help message and exit -v, --version show program's version number and exit -l, --license show license

References:
 [1] http://docs.python.org/dev/library/argparse.html