Python for循环或列表奇怪的行为 [英] Python strange behavior in for loop or lists

问题描述

我目前正在用python开发一个程序，而我刚刚注意到foreach循环在语言中出了什么问题，或者是列表结构。我只是简单地给出一个我的问题的泛型例子，因为我的程序和我的泛型例子都得到了同样的错误行为：

pre $ x = [1,2,2,2,2]

for i in x：
x.remove（i）

print x


好的，这里的问题很简单，我虽然认为这段代码应该从名单。那么，问题是执行后，我总是得到2个剩余的元素在列表中。

我做错了什么？感谢所有的帮助提前。

编辑：我不想清空一个列表，这只是一个例子... $ / $ b $在Python中，这是一个记录良好的行为，你不应该修改被迭代的列表。试试这个：

  for i in x [：]：
 x.remove（i）
  

[：] 返回一个 c $ c> x ，它恰好包含了它的所有元素，因此是 x 的副本。 b

I'm currently developing a program in python and I just noticed that something was wrong with the foreach loop in the language, or maybe the list structure. I'll just give a generic example of my problem to simplify, since I get the same erroneous behavior on both my program and my generic example:

x = [1,2,2,2,2]

for i in x:
    x.remove(i)

print x        

Well, the problem here is simple, I though that this code was supposed to remove all elements from a list. Well, the problem is that after it's execution, I always get 2 remaining elements in the list.

What am I doing wrong? Thanks for all the help in advance.

Edit: I don't want to empty a list, this is just an example...

解决方案

This is a well-documented behaviour in Python, that you aren't supposed to modify the list being iterated through. Try this instead:

for i in x[:]:
    x.remove(i)

The [:] returns a "slice" of x, which happens to contain all its elements, and is thus effectively a copy of x.

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