谁能告诉我这个index是干吗用的？
def sub_sum(L):
index = 0
sum1 = 0
sum2 = 0
for item in L:
if index % 2 == 0:
sum1 += item
else:
sum2 += item
index += 1
return sum1, sum2
L = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
result = sub_sum(L)
print('奇数项的和 = {}'.format(result[0]))
print('偶数项的和 = {}'.format(result[1]))
