argparse: from script to tool

Any .py file becomes a real CLI with a few lines of argparse. Users get --help for free.

The four kinds of arguments

1. Positional: add_argument("name") — required, no dashes.
2. Optional: add_argument("-l", "--lang") — dash-prefixed.
3. Flags: add_argument("--shout", action="store_true") — presence = True.
4. Choices: choices=["en","hi"] — argparse rejects anything else with a nice error.

Type coercion

type=int (or float, or your own function) parses + validates. Bad input → clean error, no traceback.

Making it installable

Add to pyproject.toml:

[project.scripts]
pygreet = "pygreet:main"

Then pip install . and pygreet Nitesh --lang hi works from anywhere.

Sub-commands (git-style)

sub = parser.add_subparsers(dest="cmd", required=True)
p_run = sub.add_parser("run", help="run something")
p_run.add_argument("--verbose", action="store_true")
p_deploy = sub.add_parser("deploy", help="deploy something")
p_deploy.add_argument("env")

Enables mytool run --verbose and mytool deploy prod.

When argparse isn't enough

• click — more ergonomic decorators.
• typer — click but with type hints, made by the FastAPI author.
• rich for pretty output, questionary for interactive prompts.

Try it

1. Add a --emoji flag that appends 👋.
2. Add a positional list arg for multiple names.