Chapter 22: Building CLI Tools with argparse, Click & Typer

Objectives

• Use argparse to parse arguments and options.
• Create commands and subcommands with Click.
• Leverage Typer and type hints to build CLIs.
• Package your tool as a console script.
• Handle input validation, help text and error messages.

1. argparse Basics

import argparse

def main():
    parser = argparse.ArgumentParser(description="Greet a user.")
    parser.add_argument("name", help="Name of the user")
    parser.add_argument("-t", "--times", type=int, default=1,
                        help="Number of greetings")
    args = parser.parse_args()

    for _ in range(args.times):
        print(f"Hello, {args.name}!")

if __name__ == "__main__":
    main()

Run: python chapter22.py Alice -t 3

2. Click

import click

@click.command()
@click.argument("name")
@click.option("--times", default=1, help="Number of greetings")
def cli(name, times):
    """Greet a user multiple times."""
    for _ in range(times):
        click.echo(f"Hello, {name}!")

if __name__ == "__main__":
    cli()

Install: pip install click. Run: python chapter22.py Bob --times 2

3. Typer & Type Hints

import typer

app = typer.Typer()

@app.command()
def greet(name: str, times: int = 1):
    \"\"\"Greet a user multiple times.\"\"\"
    for _ in range(times):
        typer.echo(f"Hello, {name}!")

if __name__ == "__main__":
    app()

Install: pip install typer[all]. Run: python chapter22.py greet Carol --times 3

4. Packaging CLI Tools

Add to setup.py or pyproject.toml:

[project.scripts]
mycli = "mypackage.cli:app"

After installation: mycli --help

Exercises

1. Extend the argparse example with a --uppercase flag.
2. Create a Click group with two subcommands: greet and farewell.
3. Build a Typer app with commands to add/list/remove items from an in-memory todo list.
4. Package the Typer app and install it locally as todo-cli.