Python Command Line Parsing

I have been using argparse for command line parsing, but it wasn’t until recently that I discovered it can be used to create subcommands.

General Argument Parsing

General argument parsing is quite simple. You just instantiate an argparse, and then call the object’s add argument method.

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import argparse
from argparse import RawTextHelpFormatter
parser = argparse.ArgumentParser(
    prog='program',
    description='Some description',
    formatter_class=RawTextHelpFormatter
)
parser.add_argument('-s',
                    help="description for args",
                    required=False,
                    type=str)

Subcommand Creation

Subcommands need to first create a subparser object based on the main argument parser (above is parser), and then call this object’s method to add subcommands.

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sub_parser = parser.add_subparsers(title='sub-commands',
                                    description='Some description',
                                    help='Some help description')
sub_parser_a = sub_parser.add_parser('a', help='Some help description')
sub_parser_a.add_argument('-s', 
                        help="description for args",
                        type=str)

This way, you can define subprograms under the main program. argparse also provides a method to specify a function to run when a specific subcommand is called. This function will receive all parameter values under the subcommand as a namespace and can start executing the subprogram after parsing the parameters.

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sub_parser_a.set_defaults(func=subFun)

def countFun(args):
    args = vars(args)
    print(args)

Other

argparse can also implement multiple subprograms and inherit main program parameters for subprograms. This has not been used yet, so I will update it later.