The number of days in the month of the given date

def _days_in_month(date):
    """The number of days in the month of the given date"""
    if date.month == 12:
        reference = type(date)(date.year + 1, 1, 1)
    else:
        reference = type(date)(date.year, date.month + 1, 1)
    return (reference - timedelta(days=1)).day