Argparse

The ArgumentParser object exposes an attribute that contains the value passed in from the command-line. This attribute takes its identifier from the dest keyword argument when invoking the add_argument() method.

import argparse

def get_args():
    parser = argparse.ArgumentParser()
    parser.add_argument(
        dest='bar',
        description=helptext, # (1)
    )
    return parser.parse_args()

def main():
    args = get_args().bar

1. The optional value assigned to description will be displayed when running the script with the options -h or --help

A help string can be provided as a keyword argument to help.

parser.add_argument("foo", help="bar")

A data type can be specified as an argument to type:

parser.add_argument("foo", type=int)

An alternative name for the dest value on the command-line (but which does not affect the identifier of the attribute on which the value is exposed) can be specified by metavar.

parser.add_argument("foo", metavar="bar")

The examples above used positional parameters (i.e. an argument). A named parameter (an option or flag, i.e. -h, --help, etc) requires - at the beginning of the string and values from the command-line to be passed after = or Space. add_argument supports the required keyword argument for named parameters. Note that use of the option on the command-line at all requires an argument to it, even if the option is not required itself.

parser.add_argument('-r','--radius',type=int,required=True,help='radius')

A flag option can be created by defining an action keyword parameter. (src)

parser.add_argument('-o', '--on', help='A boolean flag', action='store_true')

add_mutually_exclusive_group() can be used to add a group of mutually exclusive arguments. In this case, add_argument() is invoked on the new object returned by this method and not directly on the ArgumentParser() object.

g=ArgumentParser.add_mutually_exclusive_group()
g.add_argument("-v","--verbose", action="store_true")
g.add_argument("-q","--quiet","-s","--silent", action="store_true",help='quiet/silent mode')

User input can be restricted by providing a value for choices, which will accept any iterable value including lists, ranges, and strings:

parser.add_argument("foo", choices=["bar","baz"])
parser.add_argument("foo", choices=range(1,10))
parser.add_argument("foo", choices='Hello, world!') # equivalent to ['H','e', ...]

Sources

• Python documentation