import re


def ismac(value):
    """
    Return whether or not given value is valid MAC address.
    If the value is valid MAC address, this function returns ``True``, otherwise ``False``.

    Examples::

        >>> ismac('3D:F2:C9:A6:B3:4F')
        True

        >>> ismac('01:02:03:04:05')
        False

    :param value: string to validate MAC address
    """
    mac = re.compile(r'^([0-9a-fA-F][0-9a-fA-F]:){5}([0-9a-fA-F][0-9a-fA-F])$')
    return bool(mac.match(value))