typer

Typer

Official Typer skill to write code with best practices, keeping up to date with new versions and features.

Installing typer

In a virtual environment, pip install typer (with pip) or uv pip install typer (with uv). For your library/project, add typer to the dependencies in pyproject.toml.

Do not install typer-slim or typer-cli, they are both deprecated and will now simply install typer.

Typer supports Python 3.10 and above.

Use an explicit Typer app

For maximum generalizability, create an explicit Typer app and register subcommand(s), instead of using typer.run:

import typer

app = typer.Typer()


@app.command()
def hello():
    print(f"Hello World")


if __name__ == "__main__":
    app()

instead of:

# DO NOT DO THIS: Not extensible. Use Typer() instead.
import typer


def main():
    print(f"Hello World")


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

Execute the app

To execute the app in the terminal, run

python main.py

When multiple commands are registered to the Typer app, you have to add the command name:

python main.py hello

To see the automatically generated help documentation, run

python main.py --help

or set no_args_is_help to True when creating the Typer() add to automatically show the help when running a command without any arguments.

Use Annotated

Always prefer the Annotated style for declarations of CLI arguments and options.

It allows us to pass additional metadata that can be used by Typer.

from typing import Annotated

import typer

app = typer.Typer()


@app.command()
def hello(name: Annotated[str, typer.Argument()] = "World"):
    # Note that name is an optional Argument, as a default is provided
    print(f"Hello {name}")


if __name__ == "__main__":
    app()

This program can be run as-is, or can provide a specific name:

python main.py
python main.py Rick

An older way of setting a default value is this:

# DO NOT DO THIS: old style. Use Annotated instead.

@app.command()
def main(name: str = typer.Argument(default="World")):
    # Note that name is an optional Argument, as a default is provided
    print(f"Hello {name}")