Python period generator

gistfile1.py

from datetime import datetime
import calendar

def genDatePeriods(startDate, endDate, format='%Y-%m-%d'):
    dt1 = datetime.strptime(startDate, format)
    dt2 = datetime.strptime(endDate, format)

    for year in range(dt1.year, dt2.year + 1):
        for month in range(1, 13):
            day0 = dt1.day if month == dt1.month and year == dt1.year else 1
            day1 = dt2.day if month == dt2.month and year == dt2.year else calendar.monthrange(year, month)[1]
            if (year == dt1.year and month < dt1.month) or (year == dt2.year and month > dt2.month):
                continue
            else:
                d0 = (year, month, day0)
                d1 = (year, month, day1)
                yield [datetime(*d).strftime(format) for d in [d0, d1]]