python 计算周的范围时间

week_len = ["", 2, 3, 4]
week_time_list = ["2021-09-06", "2021-09-27"]
ne = []
print(week_time_list)
for j in range(0, len(week_len)):
    c = ne[-1] if len(ne) > 0 else week_time_list[0]
    end_date = datetime.strptime(c, '%Y-%m-%d')
    now_date_end = timedelta(days=7)
    s = end_date + now_date_end
    result_time = s.strftime('%Y-%m-%d')
    ne.append(result_time)
ne.pop()
ne.insert(0, week_time_list[0])

print(ne)
gf = [
    (item, datetime.strftime(datetime.strptime(item, '%Y-%m-%d') + timedelta(days=7), '%Y-%m-%d'))
    for item in ne]
print(gf)