Exercise 2 solution

    import re

    def is_code(s):
        return re.fullmatch(r"[A-Z]{3}-\d{4}", s) is not None

    for s in ["ABC-1234", "AB-1234", "ABC-12345", "abc-1234", "xABC-1234"]:
        print(s, is_code(s))

Output (run):
    ABC-1234 True
    AB-1234 False
    ABC-12345 False
    abc-1234 False
    xABC-1234 False

    print(bool(re.match(r"[A-Z]{3}-\d{4}", "ABC-12345")))   # True

re.match only anchors the START of the string. "ABC-1234" matches the first
eight characters, and the extra "5" is simply ignored, so a code that is too
long is wrongly accepted. fullmatch requires the pattern to cover the whole
string, so the extra digit makes it fail. (The same effect can be had with
re.search and ^...$ anchors, but fullmatch says it directly.)