Check for valid hostname

isvalidhostname.py

import re

def isvalidhostname(hostname):
    """
    Validate hostname
    """
    regex = re.compile("[^A-Z\d-]", re.IGNORECASE)

    if len(hostname) > 255:
        return False

    # A single trailing dot is legal, strip it if present
    if hostname.endswith("."):
        hostname = hostname[:-1]

    for label in hostname.split("."):
        test_1 = (label and len(label) <= 63)
        test_2 = (not label.startswith("-"))
        test_3 = (not label.endswith("-"))
        test_4 = (not regex.search(label))

        result = (test_1 and test_2 and test_3 and test_4)

        if not result:
            return result

    return result