'Return the start date of the next interval.
The interval is defined by start date <= item date < next start date.'

def _get_next_month(self, date):

    if (date.month == 12):
        return date.replace(year=(date.year + 1), month=1, day=1)
    else:
        return date.replace(month=(date.month + 1), day=1)
