如何创建python迭代器的副本？ [英] How to create a copy of python iterator?

问题描述

在python中，我尝试使用赋值创建迭代器的副本，但是它创建了一个迭代器的副本，它引用了原始迭代器本身。例如：

In python i tried to create a copy of my iterator with using assignment however it create a copy of iterator which reference to the original iterator itself. For instance:

my_list = [5, 4, 3,2]
first_it = iter(my_list)
second_it = first_it 
print next(first_it )        #it will print 5
print next(second_it)        #it will print 4
print next(first_it )        #it will print 3

正如您在示例中看到的，first_it和second_it都引用相同的迭代器对象。是否可以创建一个不参考原始对象的迭代器对象副本？

As you see in the example first_it and second_it both refer to same iterator object. Is it possible to create a copy of iterator object which is not reference to the original object?

注意
这个问题是如何按值创建迭代器对象的副本。所以不要在my_list中提及项目：就像解决方案一样。

提前谢谢

Note This question is about how to creating a copy of iterator object by value. So don't mention for item in my_list: like solutions.
Thanks in advance

推荐答案

使用 itertools.tee（）功能以生成副本;这些使用缓冲区在不同的迭代器之间共享结果：

Use the itertools.tee() function to produce copies; these use a buffer to share results between different iterators:

from itertools import tee

my_list = [5, 4, 3,2]
first_it = iter(my_list)
first_it, second_it = tee(first_it)
print next(first_it)   # prints 5
print next(second_it)  # prints 5
print next(first_it)   # prints 4

注意你不应该更长时间使用原始迭代器;只使用T恤。

Note that you should no longer use the original iterator; use only the tees.

请注意，缓冲区还意味着如果您将其中一个副本推进到其他副本之前，这些内容可能会产生巨大的内存成本！从文档：

Note that the buffer also means that these can incur a significant memory cost if you advance one of the copies far ahead of the others! From the documentation:

这个itertool可能需要大量的辅助存储（取决于需要存储多少临时数据）。通常，如果一个迭代器在另一个迭代器启动之前使用大部分或全部数据，则使用 list（）代替 tee（）会更快。

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