itertools“上一个"(与下一个相反)python [英] itertools 'previous' (opposite of next) python

问题描述

我目前正在使用

>> import itertools
>> ABC = [a, b, c]
>> abc = itertools.cycle( ABC )
>> next( abc )
a
>> next( abc )
b    
>> next( abc )
c

我希望下一个电话

>> previous( abc )
b

itertools中是否有一种方法可以做到这一点?

Is there a method in itertools that can accomplish this?

推荐答案

不，没有.

由于Python的迭代协议的工作方式，如果不保留所生成值的整个历史记录，就不可能实现previous. Python不会这样做，并且鉴于内存需求，您可能不希望这样做.

Because of the way Python's iteration protocol works, it would be impossible to implement previous without keeping the entire history of the generated values. Python doesn't do this, and given the memory requirements you probably wouldn't want it to.

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