Exercise 2 solution

    import re

    pc = re.compile(r"[A-Z]{1,2}\d[A-Z\d]? \d[A-Z]{2}")

    for s in ["EH1 1YZ", "SW1A 1AA", "M1 1AE", "eh1 1yz", "EH11 1YZ", "EH1 1Y"]:
        print(s, bool(pc.fullmatch(s)))
    # EH1 1YZ True
    # SW1A 1AA True
    # M1 1AE True
    # eh1 1yz False
    # EH11 1YZ True
    # EH1 1Y False

(All lines were run and printed exactly what is shown.)

Explanation: one or two letters, a digit, an optional letter or digit, a
space, a digit and two letters. Lower case fails because there is no
re.IGNORECASE. Note that "EH11 1YZ" passes: this shape check cannot know
which codes really exist, only that the text looks right.