问题描述
我正在使用python 3.4并只是学习基础知识，所以请多多包涵..
I'm using python 3.4 and just learning the basics, so please bear with me..
listA = [1,2]
for a in listA:
listA.remove(a)
print(listA)
假设我得到一个空列表，但是得到的是一个值为'2'的列表.我用大号调试了代码.列表中的值的组合，并且当列表具有单个元素时，for循环退出.为什么没有从列表中删除最后一个元素??
What is suppose is I get an empty list, but what I get is a list with value '2'. I debugged the code with large no. of values in list and when the list is having a single element the for loop exit.Why is the last element not removed from the list..?
推荐答案
在迭代列表时，请勿更改列表.当您删除项目时，列表的索引会更改，因此某些项目将永远不会被评估.请改用列表理解，它会创建一个新列表:
You should not change a list while iterating over it. The indices of the list change as you remove items, so that some items are never evaluated. Use a list comprehension instead, which creates a new list:
[a for a in list if ...]
换句话说，尝试这样的事情:
In other words, try something like this:
>>> A = [1, 2, 3, 4]
>>> A = [a for a in A if a < 4] # creates new list and evaluates each element of old
>>> A
[1, 2, 3]
使用for循环时，将使用内部计数器.如果在迭代list时将剩余元素向左移动，则不会评估剩余list中最左边的元素.请参见注释，了解for语句.
When you use a for-loop, an internal counter is used. If you shift the remaining elements to the left while iterating over the list, the left-most element in the remaining list will be not be evaluated. See the note for the for statement.
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