if t0iso[1] != 1:
    t0prime = t0 + datetime.timedelta(7 - t0iso[2])
else:
    t0prime = t0 - datetime.timedelta(t0iso[2])
return t0prime + datetime.timedelta(7 * (isoWeek - 1) + isoDayOfWeek)
How to derive the week start for a given (iso) weeknumber / year in python