Specify a subcommand as a command line argument in Python

Introduction

I often write commands that run on the command line in Python, but sometimes I want to write subcommands like git.

For git

$ git commit -m "test"

This commit is a subcommand.

Create this subcommand.

Implementation

If you want to parse command arguments in Python, use the ** argparse ** module.

15.4. argparse — Command line options, arguments, subcommand parsers — http://docs.python.jp/2.7/library/argparse.html?highlight=argparse#argparse

Normally, you would import the ** ArgumentParser ** class from the argparse module. Then define the parser and add options.

Normal time :

normal.py

from argparse import argumentParser

parser = ArgumentParser(description='Process some integers.')
parser.add_argument('integers', metavar='N', type=int, nargs='+',
                   help='an integer for the accumulator')
parser.add_argument('--sum', dest='accumulate', action='store_const',
                   const=sum, default=max,
                   help='sum the integers (default: find the max)')

args = parser.parse_args()
print args.accumulate(args.integers)

You need to nest parsers in order to create subcommands. ** You can set subcommands by installing another parser inside the parser. ** **

subcmd.py

>>> from argparse import ArgumentParser
>>>
>>> # create the top-level parser
>>> parser = ArgumentParser(prog='PROG')
>>> parser.add_argument('--foo', action='store_true', help='foo help')
>>> subparsers = parser.add_subparsers(help='sub-command help')
>>>
>>> # create the parser for the "a" command
>>> parser_a = subparsers.add_parser('a', help='a help')
>>> parser_a.add_argument('bar', type=int, help='bar help')
>>>
>>> # create the parser for the "b" command
>>> parser_b = subparsers.add_parser('b', help='b help')
>>> parser_b.add_argument('--baz', choices='XYZ', help='baz help')
>>>
>>> # parse some arg lists
>>> parser.parse_args(['a', '12'])
Namespace(bar=12, foo=False)
>>> parser.parse_args(['--foo', 'b', '--baz', 'Z'])
Namespace(baz='Z', foo=True)

Create a wrapper for the subparser with the parser.add_subparsers method and

subparsers = parser.add_subparsers(help='sub-command help')

Make a subparser from a wrapper.

parser_a = subparsers.add_parser('a', help='a help')

Give arguments to the subparser.

parser_a.add_argument('bar', type=int, help='bar help')

By the way, in the case of the above sample, the help message looks like this.

usage: PROG [-h] [--foo] {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
--foo       foo help

Now you can create subcommands.