How to create a list of totals for durations?

I want to calculate a bonus based on the two consecutive months where sales where the most. So I can iterate a total for every two consecutive months to find the Max value ie get

value = Max[total_between_firstdayMonth1_and_lastDayMonth2, total_between_firstdayMonth2_and_lastDayMonth3, ... , total_between_firstdaySecondToLastMonth_andlastDayLastMonth]

So I might need a list of pairs of datetime objects or something similar.

start= model.Order.order('created').get().created # get the oldest order
 end = model.Order.order('-created').get().created # get the newest order
 

So inbetween start and end I must partition the time in overlapping pairs of consecutive 2 months eg. if first order was in december 2008 and the last order was in november 2011 then the list from where to pick the max should be [total_december2008 + total_january2009, total_january2009 + total_february2009, ... , total_october2011 + total_november2011]

But then how do I get the last day of the second month if I know the start like above? How can I create the list of times and totals?

I might not be able to create the list of totals right away but if I can create the list of starts and ends then I can call a helper function we can assume eg.

total(start_datetime, end_datetime)

Thanks for any help

Update

I think I found how to calculate the time for an example interval where the timeline is from any date to last day next month:

>>> d = date(2007,12,18)
 >>> print d
 2007-12-18
 >>> d + relativedelta(months=2) - timedelta(days=d.day)
 datetime.date(2008, 1, 31)
 

Update 2

I can calculate upto the first level the first duration. Now I only have to generalize it to loop through all the durations and check which was the highest level:

def level(self):
     startdate = model.Order.all().filter('status =', 'PAID').filter('distributor_id =' , self._key.id()).get().created.date()
     last_day_nextmonth =startdate + relativedelta(months=2) - timedelta(days=1)
     if self.personal_silver(startdate, last_day_nextmonth) + self.non_manager_silver(startdate, last_day_nextmonth) < 25:
         maxlevel = _('New distributor')
     elif self.personal_silver(startdate, last_day_nextmonth) + self.non_manager_silver(startdate, last_day_nextmonth)   > 25:
         maxlevel = _('Assistant Teamleader')
     return maxlevel
 

Update 3

Closer to what I mean is taking the max of some function values from beginning up to now. Basecase can be that last day next month is is the future and the helper function can be recursive but I didn't have time or help to make it recursive to it only works for the first 2 periods now ie 4 months from start:

def level(self):
     startdate = model.Order.all().filter('status =', 'PAID'
             ).filter('distributor_id =',
                      self._key.id()).get().created.date()
     last_day_nextmonth = startdate + relativedelta(months=2) \
         - timedelta(days=1)
     total = self.personal_silver(startdate, last_day_nextmonth) + self.non_manager_silver(startdate, last_day_nextmonth)
     if total >= 125:
         level = 5
     elif total >= 75:
         level = 4
     elif total >= 25:
         level = 3
     elif total >= 2:
         level = 2
     else:
         level = 1
     return self.levelHelp(level, last_day_nextmonth + timedelta(days=1))
 
 def levelHelp(self, level, startdate):
     #if startdate in future return level
     last_day_nextmonth = startdate + relativedelta(months=2) \
         - timedelta(days=1)
     total = self.personal_silver(startdate, last_day_nextmonth) + self.non_manager_silver(startdate, last_day_nextmonth)
     if total >= 125:
         newlevel = 5
     elif total >= 75:
         newlevel = 4
     elif total >= 25:
         newlevel = 3
     elif total >= 2:
         newlevel = 2
     else:
         newlevel = 1
     return level if level > newlevel else newlevel
 

Update 4

I added the recursion where base case is that next step is in the future, if so it will return the max level:

def level(self):
     startdate = model.Order.all().filter('status =', 'PAID'
             ).filter('distributor_id =',
                      self._key.id()).get().created.date()
     last_day_nextmonth = startdate + relativedelta(months=2) \
         - timedelta(days=1)
     total = self.personal_silver(startdate, last_day_nextmonth) + self.non_manager_silver(startdate, last_day_nextmonth)
     if total >= 125:
         level = 5
     elif total >= 75:
         level = 4
     elif total >= 25:
         level = 3
     elif total >= 2:
         level = 2
     else:
         level = 1
     return self.levelHelp(level, last_day_nextmonth + timedelta(days=1))
 
 def levelHelp(self, level, startdate):
 
     last_day_nextmonth = startdate + relativedelta(months=2) \
         - timedelta(days=1)
     total = self.personal_silver(startdate, last_day_nextmonth) + self.non_manager_silver(startdate, last_day_nextmonth)
     if total >= 125:
         newlevel = 5
     elif total >= 75:
         newlevel = 4
     elif total >= 25:
         newlevel = 3
     elif total >= 2:
         newlevel = 2
     else:
         newlevel = 1
 
     maxlevel = level if level > newlevel else newlevel
 
     nextstart = last_day_nextmonth + timedelta(days=1)
     now = datetime.now().date()
     if nextstart > now: #next start in is the future
         return maxlevel
     else: return self.levelHelp(maxlevel, nextstart)
 

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