fastapi/typer

Typer is a Python library for building command-line interface (CLI) tools, programs that run in a terminal and accept commands and options like "myapp deploy --env production". The problem it solves is that writing CLI tools in Python has traditionally required a lot of boilerplate: you have to manually define arguments, write help text, handle errors, and set up tab-completion. Typer makes this nearly effortless by reading your standard Python function signatures and type annotations to figure out all of that automatically. For example, a plain Python function that takes a "name" argument becomes a CLI command with proper help text, error messages for missing arguments, and shell auto-completion, with almost no extra code. You can build simple single-command tools or complex multi-command CLIs with subcommands by just decorating functions. Typer also ships with a "typer" command-line tool that can run any plain Python script as a CLI app even if it does not use Typer directly. It is built on top of Click (a popular Python CLI library) and integrates with the Rich library for colorful, well-formatted terminal output. You would use Typer whenever you want to turn a Python script into a user-friendly command-line tool for yourself, your team, or as part of a Python package. The stack is Python 3 with type hints.