import re


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

    Examples::

        >>> islongitude('+73.234')
        True

        >>> islongitude('180.1')
        False

    :param value: string to validate longitude
    """
    long = re.compile(r'^[-+]?(180(\.0+)?|((1[0-7]\d)|([1-9]?\d))(\.\d+)?)$')
    return bool(long.match(value))