Typer and __init__

Use Typer to turn classes into CLIs.

Typer

Typer is a fantastic python library for quickly turning functions into CLIs, built by the folks behind FastAPI. A minimal example:

import typer


def add(a: float, b: float) -> float:
    '''Adds two numbers and returns the results'''
    return a + b


if __name__ == '__main__':
    typer.run(add)

There are loads more patterns and examples in the official documentation.

__init__

If you'd like, you can serve a class with a typed __init__ method:

import typer


class Addor:
    '''Addor: Adds two numbers and print the result'''
    def __init__(self, a: float, b: float):
        print(a + b)


if __name__ == '__main__':
    typer.run(Addor)

dataclasses

I love this pattern for defining CLI commands with dataclasses. The parameters and type info are all up front. Defaults are clear and legible. Personally I think this reads really cleanly.

import dataclasses

import typer


@dataclasses.dataclass
class Addor:
    '''Addor: Adds two numbers and print the result'''
    a: float
    b: float

    def __post_init__(self):
        print(self.a + self.b)


if __name__ == '__main__':
    typer.run(Addor)

typer.Typer

In case you were wondering, this works as well:

import dataclasses

import typer


app = typer.Typer()

@app.command()
@dataclasses.dataclass
class Addor:
    '''Addor: Adds two numbers and print the result'''
    a: float
    b: float

    def __post_init__(self):
        print(self.a + self.b)


if __name__ == '__main__':
    app()