Return the week corresponding to the proleptic Gregorian ordinal,
        where January 1 of year 1 starts the week with ordinal 1.

def fromordinal(cls, ordinal):
        """Return the week corresponding to the proleptic Gregorian ordinal,
        where January 1 of year 1 starts the week with ordinal 1.
        """
        if ordinal < 1:
            raise ValueError("ordinal must be >= 1")
        return super(Week, cls).__new__(cls, *(date.fromordinal((ordinal-1) * 7 + 1).isocalendar()[:2]))