hello.py

import argparse

def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("version", type=str, nargs="?", default=None)
    args = parser.parse_args()
    
    if args.version is not None:
        print(f"Installing version {args.version}")
    else:
        print("Installing latest version")
    
if __name__ == "__main__":
    main()