如何通过生成器或其他方法无限循环Python中的迭代器? [英] How can I infinitely loop an iterator in Python, via a generator or other?

问题描述

据我了解，使用Generator是实现此类目标的最佳方法，但我愿意接受建议.

It's my understanding that using a Generator is the best way to achieve something like this, but I'm open to suggestions.

具体来说，一个用例是:我想在另一个列表的旁边打印任意长度的某些项目，并在必要时截断初始迭代器.

Specifically, one use case is this: I'd like to print some items alongside another list, of an arbitrary length, truncating the initial iterator as necessary.

这里正在运行的python代码演示了我想要的确切示例行为:

Here is working python code that demonstrates the exact example behavior I desire:

    def loop_list(iterable):
        """
        Return a Generator that will infinitely repeat the given iterable.

        >>> l = loop_list(['sam', 'max'])
        >>> for i in range(1, 11):
        ...     print i, l.next()
        ... 
        1 sam
        2 max
        3 sam
        4 max
        5 sam
        6 max
        7 sam
        8 max
        9 sam
        10 max

        >>> l = loop_list(['sam', 'max'])
        >>> for i in range(1, 2):
        ...     print i, l.next()
        ... 
        1 sam
        """
        iterable = tuple(iterable)
        l = len(iterable)
        num = 0
        while num < l:
            yield iterable[num]
            num += 1
            if num >= l:
                num = 0

问题/我的问题

您可能已经注意到，这仅适用于实现__getitem__的列表/元组/可迭代对象(如果我没记错的话).理想情况下，我希望能够传递任何可迭代的对象，并接收可以正确循环其内容的生成器.

The Problem / My Question

As you may have noticed, this only works on lists/tuples/iterables that implement __getitem__ (if I'm not mistaken). Ideally, I'd like to be able to pass any iterable, and receive a generator that can properly loop over it's content.

如果有更好的方法来执行这样的操作，不使用，我也很好.

If there's a better way to do something like this without a generator, I'm fine with that as well.

推荐答案

您可以使用 itertools.cycle (链接页面上包含源代码).

You can use itertools.cycle (source included on linked page).

import itertools

a = [1, 2, 3]

for element in itertools.cycle(a):
    print element

# -> 1 2 3 1 2 3 1 2 3 1 2 3 ...

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