Libraries are collections of shared code. They're common in Python, where they're also called "modules," but they're also ...

With a command-line switch, you can see at a glance all the Python interpreters you’ve installed and then invoke a specific version, whether it’s 32-bit or 64-bit.

The idea is pretty simple. Nearly all command line Python programs use argparse to simplify picking options and arguments off the command line as well as providing some help.