pallets/click

Click is a Python package for creating command line interfaces, the text-based menus and commands you run in a terminal window, like git commit or npm install. Building these from scratch usually involves a lot of tedious code to parse user input, validate options, and display help messages. Click handles all of that for you automatically. The way it works is through a decorator-based approach (decorators in Python are annotations that add behavior to functions without rewriting them). You write a normal Python function, add a few Click decorators to declare what options or arguments it accepts, and Click turns that function into a fully working command with automatic help pages, input prompting, and error handling. Key features include the ability to nest commands together (so you can build tools like myapp create user or myapp delete project), automatic generation of --help output, and support for lazily loading subcommands only when needed, which keeps startup fast for large tools. The example in the README shows a greeting command that accepts a --count option and a --name option; if the user forgets to supply a name, Click automatically prompts them for it. You would use Click whenever you need to build a command line tool in Python and want to avoid writing the repetitive scaffolding yourself. It is written in Python and maintained by the Pallets organization.