Arguments with argparse

Menus hard-code the conversation. Arguments let users speak first:

python todo.py add "buy milk"
python todo.py list

The stdlib module for this is argparse — here is the beginner slice:

import argparse

parser = argparse.ArgumentParser(description="Todo CLI")
parser.add_argument("action", choices=["add", "list", "done"])
parser.add_argument("text", nargs="?")     # optional extra word(s)
args = parser.parse_args()

print(args.action, args.text)

parse_args() reads sys.argv for you, validates choices, and even prints usage help with -h. Wrong usage exits with a clear error instead of crashing with a traceback — professional behavior for free.