argparse: Create a Command-line App with Python

argparse is a Python standard library makes it easy to write a CLI application. You should use this module instead of optparse which is deprecated since Python 2.7.

ref:
https://docs.python.org/3/library/argparse.html

Basic example

#!/usr/bin/env python

from __future__ import print_function

import argparse
import sys

import jokekappa

class JokeKappaCLI(object):

    def __init__(self):
        parser = argparse.ArgumentParser(
            prog='jokekappa',
            description='humor is a serious thing, you should take it seriously',
        )
        self.parser = parser
        self.parser.add_argument('-v', '--version', action='version', version=jokekappa.__version__)

        self.subparsers = parser.add_subparsers(title='sub commands')
        self.subparsers \
            .add_parser('one', help='print one joke randomly') \
            .set_defaults(func=self.tell_joke)
        self.subparsers \
            .add_parser('all', help='print all jokes') \
            .set_defaults(func=self.tell_jokes)
        self.subparsers \
            .add_parser('update', help='update jokes from sources') \
            .set_defaults(func=self.update_jokes)

    def parse_args(self):
        if len(sys.argv) == 1:
            namespace = self.parser.parse_args(['one', ])
        else:
            namespace = self.parser.parse_args()
        namespace.func()

    def tell_joke(self):
        joke = jokekappa.get_joke()
        print(joke['content'])

    def tell_jokes(self):
        for joke in jokekappa.get_jokes():
            print(joke['content'])

    def update_jokes(self):
        jokekappa.update_jokes()
        print('Done')

def main():
    JokeKappaCLI().parse_args()

if __name__ == '__main__':
    main()

ref:
https://github.com/CodeTengu/JokeKappa
https://stackoverflow.com/questions/5176691/argparse-how-to-specify-a-default-subcommand

Advanced example

In following code, you're able to create a Python module called pangu and a command-line tool also called pangu, both share the same codebase.

in pangu.py

from __future__ import print_function

import argparse
import sys

__version__ = '3.3.0'
__all__ = ['spacing_text', 'PanguCLI']

def spacing_text(text):
    """
    You could find real code in https://github.com/vinta/pangu.py
    """
    return text.upper().strip()

class PanguCLI(object):

    def __init__(self):
        parser = argparse.ArgumentParser(
            prog='pangu',
            description='paranoid text spacing',
        )
        self.parser = parser
        self.parser.add_argument('-v', '--version', action='version', version=__version__)
        self.parser.add_argument('text', action='store', type=str)

    def parse(self):
        if not sys.stdin.isatty():
            print(spacing_text(sys.stdin.read()))
        elif len(sys.argv) > 1:
            namespace = self.parser.parse_args()
            print(spacing_text(namespace.text))
        else:
            self.parser.print_help()
        sys.exit(0)

if __name__ == '__main__':
    PanguCLI().parse()

in bin/pangu

#!/usr/bin/env python

from pangu import PanguCLI

if __name__ == '__main__':
    PanguCLI().parse()

in setup.py

from setuptools import setup

setup(
    name='pangu',
    py_modules=['pangu', ],
    scripts=['bin/pangu', ],
    ...
)

As a result, there're multiple usages:

$ pangu "abc"
$ python -m pangu "abc"
$ echo "abc" | pangu
$ echo "abc" | python -m pangu
ABC

ref:
https://github.com/vinta/pangu.py

Accept a list as option

parser.add_argument('-u', '--usernames', type=lambda x: x.split(','), dest='usernames', required=True)
# your_command -u vinta
# your_command -u vinta,saiday

Accept conditional argument

ref:
https://stackoverflow.com/questions/15459997/passing-integer-lists-to-python

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