argparse¶

Command Line Arguments

The argparse module enables the parsing of command line arguments.

argparse Documentation

Example Usage

python main.py -i input.txt -o output.txt --verbose

Defining Arguments¶

Arguments are defined by creating an ArgumentParser object and adding arguments to it.

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('-i', '--input', help='Input file')
parser.add_argument('-o', '--output', help='Output file')

Input Parameters for `ArgumentParser.add_argument()`¶

Parameter	Description	Values
`...`	Name or flags of the argument.
`action`	How argument should be handled.	`store`, `store_const`, `store_true`, `append`, `append_const`, `count`, `help`, `version`
`choices`	List of allowed values.	`List[str]`, `range(1,10)`, `Container`
`default`	Default value if argument is not provided	Default: `None`
`const`	Value to be used for `store_const`	If flag is set, store `const` value
`help`	Help text for the argument.
`type`	Type of the argument.
`required`	Whether the argument is required.	`True` or `False`
`nargs`	Number of times argument can be reused	`int`, `?`, `*`, `+`

action

Value	Description
`store`	Store the argument value in the `args` namespace.
`store_const`	Store the value specified by `const` in the `args` namespace.
`store_true`	Store the value `True` in the `args` namespace.
`append`	Append the value to a list, useful for multiple argument use.
`append_const`	Append the value specified by `const` to a list.
`count`	Count the number of times the argument is used.
`help`	Print help text and exit.
`version`	Print version text and exit.

Example Usage

parser.add_argument(
    '-i', '--input',
    action='store',
    choices=['a', 'b', 'c'],
    default='a',
    type=str,
    required=True,
    nargs=1,
    help='Input file'
    )

python main.py -i a
python main.py --input a

### parser.input = 'a'

Positional Arguments¶

Postitional arguments are arguments which are not preceded by a flag. They get interpreted in the order they are defined. Normally, positional arguments are used for required arguments.

parser.add_argument('input')

python main.py input

Optional Arguments¶

Optional arguments are arguments which are preceded by a flag. They can be used in any order.

parser.add_argument("--optional_arg", type=str, help="optional")

python main.py --optional_arg

Argument with Value¶

Arguments can be defined with a value. The value can be accessed by the args namespace.

parser.add_argument("--value", type=int, choices=range(1,10+1))

python main.py --value 2

Argument Shortcuts¶

add_argument can take multiple flags for the same flag.

parser.add_argument("-i", "--input", type=str)

python main.py -i test
python main.py --input test

Help¶

Argparse adds -h and --help flags by default.

python main.py --help

Subparser¶

If argparse should solve multiple different problems/tasks subparsers are a great solution. For each sub task we can define a subparser.

Add subparser to the main parser:

import argparse

parser = argparse.ArgumentParser()
subparser = parser.add_subparsers(dest="command")

Create two differen parsers for differend usecases:

add = subparser.add_parser("add")
rm = subparser.add_parser("del")

Now we can get the specified command over the argparse Namespace from command:

args = parser.parse_args()

if args.command == "add":
    print("add")
elif args.command == "del":
    print("delete")