Getting start/end dates given week-number

[Tim Chase]

I've been trying to come up with a good algorithm for determining 
the starting and ending dates given the week number (as defined 
by the strftime("%W") function).

My preference would be for a Sunday->Saturday range rather than a 
Monday->Sunday range.  Thus,

 >>> startDate, stopDate = weekBoundaries(2006, 23)

would yield a start-date of June 4, 2006 and an end-date of June 
10, 2006 in this hypothetical function (as strftime("%W") for 
today, June 9th, 2006 returns 23).

I've posted my first round of code below, but I'm having problems 
with dates early in 2005, as the tests show.

Any thoughts/improvements/suggestions would be most welcome.

Thanks,

-tkc


from datetime import date, timedelta
from time import strptime
DEBUG = False
tests = [
     #test date        start           end
     (date(2006,1,1), (date(2006,1,1), date(2006,1,7))),
     (date(2006,1,2), (date(2006,1,1), date(2006,1,7))),
     (date(2006,1,3), (date(2006,1,1), date(2006,1,7))),
     (date(2006,1,4), (date(2006,1,1), date(2006,1,7))),
     (date(2006,1,5), (date(2006,1,1), date(2006,1,7))),
     (date(2006,1,6), (date(2006,1,1), date(2006,1,7))),
     (date(2006,1,7), (date(2006,1,1), date(2006,1,7))),
     (date(2006,1,8), (date(2006,1,8), date(2006,1,14))),
     (date(2005,1,1), (date(2004,12,26), date(2005,1,1))),
     (date(2005,1,2), (date(2005,1,2), date(2005,1,8))),
     ]
def weekBoundaries(year, week):
     startOfYear = date(year, 1, 1)
     now = startOfYear + timedelta(weeks=week)
     # isoweekday() % 7 returns Sun=0 ... Sat=6
     sun = now - timedelta(days=now.isoweekday() % 7)
     sat = sun + timedelta(days=6)
     if DEBUG:
         print "DEBUG: now = %s/%s" % (now, now.strftime("%a"))
         print "DEBUG: sun = %s/%s" % (sun, sun.strftime("%a"))
         print "DEBUG: sat = %s/%s" % (sat, sat.strftime("%a"))
     return sun, sat

for test, expectedResult in tests:
     print "Testing %s" % test
     year = test.year
     # jigger it so that %W is Sun->Sat rather than Mon->Sun
     weekNum = int((test + timedelta(days=1)).strftime("%W")) - 1
     results = weekBoundaries(year, weekNum)
     passed = (expectedResult == results)
     print "Week#%s: %s" % (weekNum, passed)
     print "=" * 50