writing-cli-scripts

name	writing-cli-scripts
description	Uses typer for all Python CLI argument parsing instead of argparse. Use whenever creating a Python script that accepts command-line arguments, options, or subcommands.

CLI Scripts with Typer

Always use typer instead of argparse for CLI argument parsing.

Single command script

import typer
from pathlib import Path


def main(
    input_path: Path,
    output_path: Path = Path("output"),
    verbose: bool = False,
):
    """Process data from input path."""
    ...


if __name__ == "__main__":
    typer.run(main)

Multiple subcommands

import typer

app = typer.Typer()


@app.command()
def train(config: Path, epochs: int = 100):
    """Train the model."""
    ...


@app.command()
def evaluate(checkpoint: Path, split: str = "test"):
    """Evaluate a trained model."""
    ...


if __name__ == "__main__":
    app()

Key rules

• Use Python type hints for all parameters (typer derives CLI types from them).
• Use Path for file/directory arguments, not str.
• Positional parameters become CLI arguments; parameters with defaults become --options.
• Add a docstring to each command function for --help text.
• Exception: scripts with no arguments or a single trivial argument may skip typer.