def parse_urn(urn):
    """
    Parses a URN, returning a pair that contains a list of URN namespace parts, followed by the
    URN's unique ID.
    """
    if not urn.startswith("urn:"):
        return None

    parts = urn[len("urn:") :].split(":")
    return (parts[0 : len(parts) - 1], parts[len(parts) - 1])