A python script template with no dependencies.

script-template.py

#!/usr/bin/env python3

import argparse


class CommandError(Exception):
    pass


def main(args):
    if args.cake == "chocolate":
        raise CommandError("Not chocolate cake!")

    print(f"Yes {args.cake} cake!")


if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument("cake")

    try:
        main(parser.parse_args())
    except CommandError as e:
        print(str(e))
        exit(1)