Clak

Clak (Command Line avec Klass) is a Python library for building command-line interfaces with a class-based API on top of standard argparse. Nested commands, arguments, and optional batteries (views, logging, config, completion) stay close to what you already know from the stdlib.

Full docs: mrjk.github.io/python-clak · PyPI: mrjk.clak

Features

• Class-based CLI — define apps with Parser, Argument, and Command; no new DSL
• Argparse-native — same argument syntax as add_argument() / subparsers
• Nested commands — git-like trees with inheritance and a command overview in --help
• Optional components — views, logging, XDG config, shell-completion script generation
• Light core; extras only when you need them (colors, config, markdown, rst)

Requirements

• Python 3.10–3.14 (declared >=3.10,<4.0; CI and local matrix cover 3.10–3.14)
• argparse (stdlib)

Developer setup and the version matrix: Development setup.

Install

pip install mrjk.clak

# Or with your project manager
poetry add mrjk.clak
pdm add mrjk.clak
uv add mrjk.clak

Optional:

pip install 'mrjk.clak[colors]'   # coloredlogs for LoggingOptMixin
pip install 'mrjk.clak[config]'   # PyYAML for YAML config / --format yaml
pip install 'mrjk.clak[markdown]' # rich for MarkdownView and colored --help
pip install 'mrjk.clak[rst]'      # docutils for RstView

Quick start

from clak import Argument, Command, Parser


class ShowCommand(Parser):
    """Show something."""

    target = Argument("--target", "-t", help="Target to show")
    format = Argument(
        "--format", choices=["json", "text"], help="Output format"
    )

    def cli_run(self, target=None, format=None, **_):
        print(f"show target={target} format={format}")


class MainApp(Parser):
    """Demo application."""

    debug = Argument("--debug", action="store_true", help="Enable debug mode")
    config = Argument("--config", "-c", help="Config file path")

    show = Command(ShowCommand, help="Show something")


# Instantiating the root parser parses argv and runs the matching command.
if __name__ == "__main__":
    MainApp()

$ python demo.py --help
usage: demo.py [-h] [--debug] [--config CONFIG] {show} ...

Key concepts

Arguments

class MyCommand(Parser):
    verbose = Argument("-v", "--verbose", action="store_true", help="Verbose")

Nested commands

Command binds a child Parser (aliases: SubParser, SubCommand, Cmd):

class MainApp(Parser):
    status = Command(StatusCommand, help="Show status")

Optional components

Learn more

• Installation and Quickstart
• Guides under docs/ / the site Guides tab
• Pasteable AI context: primer · reference
• Runnable examples in examples/
• Planned work: Roadmap

Contributing

Bug reports, questions, and PRs are welcome. See the contribution guidelines in the documentation (or CONTRIBUTING.md).

License

GPL v3.