python3列表生成式中的for循环与普通放在外面的for循环细微差异
实例：
给定列表alist = [1,2,3,4,5,6,7]，k=3
想要使用for循环达成输出[5,6,7,1,2,3,4]
1.用外面的for循环做：

alist = [1,2,3,4,5,6,7]
k = 3
for _ in range(k):alist[0:0] = [alist.pop()] # 依次取出7,6,5,先取先放
print(alist)

得到：# 依次取出7,6,5,先取先放
[5, 6, 7, 1, 2, 3, 4]
2.用列表生成式的for循环：

alist = [1,2,3,4,5,6,7]
k = 3
alist[0:0] = [alist.pop() for _ in range(k)]
print(alist)

得到:
[7, 6, 5, 1, 2, 3, 4]

消除差异:
可以利用列表生成式先排列成list后才赋值的这一特性，先从倒数第K（3）个开始pop，就可以达到相同的效果:

alist = [1,2,3,4,5,6,7]
k = 3
alist[0:0] = [alist.pop(-i) for i in range(k,0,-1)]
print(alist)

结果：
[5, 6, 7, 1, 2, 3, 4]