click

  click is a Python package for creating beautiful command line interfaces
  in a composable way with as little amount of code as necessary.  It's the
  "Command Line Interface Creation Kit".  It's highly configurable but comes
  with good defaults out of the box.

  It aims at making writing command line tools fun and quick without causing
  user frustration at not being able to implement an intended CLI API.

  Click in three points:
  
  -   arbitrary nesting of commands
  -   automatic help page generation
  -   supports lazy loading of subcommands at runtime  

  Read the docs at http://click.pocoo.org/