Regex for [a-zA-Z0-9\-] with dashes allowed in between but not at the start or end

Question

Update:

This question was an epic failure, but here\'s the working solution. It\'s based on Gumbo\'s answer (Gumbo\'s was close to working so I chose it as the accepte

Answer 1

The current regex is simple and fairly readable. Rather than making it long and complicated, have you considered applying the other constraints with normal Python string processing tools?

import re

def fits_pattern(string):
    if (4 <= len(string) <= 25 and
        "--" not in string and
        not string.startswith("-") and
        not string.endswith("-")):

        return re.match(r"[a-zA-Z0-9\-]", string)
    else:
        return None