day_generator.py

import datetime

def _parse_date(d):
    if isinstance(d, datetime.date):
        return d
    elif isinstance(d, datetime.datetime):
        return d.date()
    else:
        return datetime.datetime.strptime(d, '%Y-%m-%d').date()

def day_generator(start_date=None, end_date=None, skip=1):
    if start_date is None:
        d = datetime.date.today()
    else:
        d = _parse_date(start_date)

    if end_date is not None:
        end_date = _parse_date(end_date)

    def _in_range(d):
        if end_date is None:
            return True

        if skip > 0 and d > end_date:
            return False

        if skip < 0 and d < end_date:
            return False

        return True

    while _in_range(d):
        yield d
        d += datetime.timedelta(days=skip)

def main():
    for day in day_generator('2014-03-01', '2014-03-10'):
        print day

    print

    for day in day_generator('2014-11-16', '2014-10-31', -4):
        print day

if __name__ == "__main__":
    main()