python的一个for 与 if 嵌套问题

Question

代码如下：

s= ["adam","xxx","lisa"]

L= ["adam","xxx","lisa","bart"]

for x in L:

print "this is ---%s" % x
if x in s:
    print x
    L.remove(x)

print L

结果如下：
this is ---adam
adam
this is ---lisa
lisa

['xxx', 'bart']
[Finished in 0.2s]

为何'xxx'直接被无视了？？？

Answer 1

程序运行如下

循环1，x指向L中的adam：
打印 this is ---adam
打印 adam
移除了L中的adam，x指向L中的xxx
循环完毕，x继续往下走，指向L中的lisa

循环2，x指向L中的lisa
打印 this is ---lisa
打印 lisa
移除了L中的lisa，x指向L中的bart
循环完毕，x继续往下走，走不下去了，整个循环结束

Answer 2

不是被无视了，而是位置变了

Answer 3

这么写看你能否理解（python3）：

s = ["adam", "xxx", "lisa"]
L = ["adam", "xxx", "lisa", "bart"]
for x in L[:]:
    print("this is ---%s" % x)
    if x in s:
        print(x)
        L.remove(x)
print(L)

输出

this is ---adam
adam
this is ---xxx
xxx
this is ---lisa
lisa
this is ---bart
['bart']