Exercise 2 solution

    import re
    pat = r"^(?=.*[a-z])(?=.*\d)(?!.*\s).{6,10}$"

    for s in ["abc123", "ABC123", "abcdef", "abc 123", "a1"]:
        print(repr(s), bool(re.fullmatch(pat, s)))
    # 'abc123' True
    # 'ABC123' False
    # 'abcdef' False
    # 'abc 123' False
    # 'a1' False

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

Explanation: each lookahead is tested from the start of the string and
consumes nothing. (?=.*[a-z]) needs a lowercase letter somewhere,
(?=.*\d) needs a digit, and (?!.*\s) forbids any whitespace. The final
.{6,10} then matches the whole string and enforces the length.
"ABC123" fails the lowercase check, "abcdef" the digit check, "abc 123"
the no-space check and "a1" the length.