Convert 6 bytes into a MAC string.

    Args:
        bin (str): hex string of lenth 6.

    Returns:
        str: String representation of the MAC address in lower case.

    Raises:
        Exception: if ``len(bin)`` is not 6.

def bin_to_mac(bin, size=6):
    """Convert 6 bytes into a MAC string.

    Args:
        bin (str): hex string of lenth 6.

    Returns:
        str: String representation of the MAC address in lower case.

    Raises:
        Exception: if ``len(bin)`` is not 6.
    """
    if len(bin) != size:
        raise Exception("Invalid MAC address: %s" % (bin))
    return ':'.join([binascii.hexlify(o) for o in bin])