t0 = datetime.datetime(2004, 12, 26, 0, 0, 0)
t1 = datetime.datetime(2005, 1, 10, 0, 0, 0)
ndays = (t1 - t0).days + 1
for i in range(ndays):
    d0 = t0 + datetime.timedelta(i)
d0iso = d0.isocalendar()
if d0 != isoWeekToGregorian(d0iso[0], d0iso[1], d0iso[2]):
    print('failed: %s' % d0)
else:
    print(d0, d0iso)
How to derive the week start for a given (iso) weeknumber / year in python