Python不同方式正倒序遍历的时间开销

from timeit import timeit
li = [i for i in range(1000000)]

def for_loop(n):
    # 使用for直接遍历
    ret = 0
    for i in li:
        ret = li[i]

def for_loop_enumerate(n):
    # 使用enumerate进行遍历
    ret = 0
    for idx, i in enumerate(li):
        ret = li[idx]

def reverse_loop(n):
    # 使用reversed生成迭代器进行倒序遍历li
    ret = 0
    for i in reversed(li):
        ret = li[i]

def reverse_range(n):
    # 使用range进行倒序遍历li
    ret = 0
    for i in range(len(li)-1, -1, -1):
        ret = li[i]


for_loop_time = timeit('for_loop(1000000)', setup='from __main__ import for_loop, li', number=100)
for_loop_enumerate_time = timeit('for_loop_enumerate(1000000)', setup='from __main__ import for_loop_enumerate, li', number=100)
reverse_loop_time = timeit('reverse_loop(1000000)', setup='from __main__ import reverse_loop, li', number=100)
reverse_range_time = timeit('reverse_range(1000000)', setup='from __main__ import reverse_range, li', number=100)

print(f"for_loop_time: {for_loop_time}\n\
        for_loop_enumerate_time: {for_loop_enumerate_time}\n\
        reverse_loop_time: {reverse_loop_time}\n\
        reverse_range_time: {reverse_range_time}")
# for_loop_time: 1.3836041999747977
# for_loop_enumerate_time: 2.5846562000224367
# reverse_loop_time: 1.3863778999075294
# reverse_range_time: 1.8969372999854386

可以看到，enumerate会稍微慢点。
reversed和直接遍历没有区别，反而用range倒序遍历的时候满了一点点

注意reversed返回的是个迭代器，不要想着赋值重用(对没错就是我...)