如何在循环列表本身而不删除列表时删除列表元素 [英] How to delete list elements while cycling the list itself without duplicate it

问题描述

在此Python中，我花了一点时间进行声明:

I lost a little bit of time in this Python for statement:

class MyListContainer:
    def __init__(self):
        self.list = []

    def purge(self):
        for object in self.list:
            if (object.my_cond()):
                self.list.remove(object)
        return self.list

container = MyListContainer()

# now suppose both obj.my_cond() return True
obj1 = MyCustomObject(par)
obj2 = MyCustomObject(other_par)

container.list = [obj1, obj2]

# returning not an empty list but [obj2]
container.purge()

它没有按我预期的那样工作，因为当清除"中的循环删除列表中的第一个对象时，第二个对象移到列表的开头，循环结束.

It doesn't work as I expected because when the cycle in "purge" delete the first object in list the second one is shifted to the beginning of the list and the cycle is ended.

我解决了在for循环之前复制self.list的问题:

I solved duplicating self.list before the for cycle:

...
local_list = self.list[:]
for object in local_list:
...

我想for语句停止工作，因为我正在更改原始列表的长度.有人可以澄清这一点吗?

I suppose that the for statement stop working because I'm changing the length of the original list. Can someone clarify this point ?

还有没有更优雅"的方法来解决此问题?如果列表中元素过多，那么每次都复制它似乎不是一个好主意.

And is there a more "elegant" way to solve this problem ? If I have more than few elements inside the list, duplicating it every time does not seem a good idea.

也许filter()函数是正确的，但我希望有其他方法(如有).

Maybe the filter() function is the right one but i whish to have some other approach if any.

我是新手.

总结您的有用答案:

• 永远不要编辑您要循环播放的列表
• 复制列表或使用列表理解
• 复制列表不会浪费您的内存，在这种情况下，谁会介意

推荐答案

过滤器(或列表理解)是解决之道.如果您想就地执行此操作，则可以执行以下操作:

Filter (or list comprehension) IS the way to go. If you want to do it inplace, something like this would work:

purge = []
for i,object in enumerate(self.list):
    if object.mycond()
        purge.append(i)
for i in reversed(purge):
    del self.list[i]

或者，可以通过理解来创建清除列表，快捷方式如下:

Or alternatively, the purge list can be made with a comprehension, a shortcut version looks like:

for i in reversed([ i for (i,o) in enumerate(self.list) if o.mycond() ]):
    del self.list[i]

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