Hostname and IPv4 address validation in Python

def isValidHostname(hostname):
    if len(hostname) > 255:
        return False
    if hostname[-1] == ".":
        hostname = hostname[:-1]
    allowed = re.compile("(?!-)[A-Z\d-]{1,63}(?<!-)$", re.IGNORECASE)
    return all(allowed.match(x) for x in hostname.split("."))

def isValidIPv4Address(ipaddress):
    return re.match(r"^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$",ipaddress)