@classmethod
def isWeekly(cls, expiration):
    """isWeekly checks if the expiration date corresponds to a Weekly
        SPX option.

        Weeklys were introduced in 2005, but had a very low liquidity for many
        years. The CBOE itself did not include Weeklys in the computation of
        the VIX until after 2013 (in 2014 Weeklys were included). For this
        reason, when selecting options it is often argued that Weeklys
        prior to 2014 should be disconsidered.

        Args:
            expiration (datetime): A datetime object containing the expiration
                       date of the option. Must have year, month and
                       day.

        Returns:
            (bool): True if Weekly SPX option.

        """
    return not cls.isStandard(expiration)
