itertools中chain和chain.from_iterable有什么区别?

问题描述

我在互联网上找不到任何有效的例子，我可以看到它们之间的区别以及为什么要选择一个而不是另一个.

I could not find any valid example on the internet where I can see the difference between them and why to choose one over the other.

推荐答案

第一个接受 0 个或多个参数，每个参数是一个可迭代对象，第二个接受一个预期生成可迭代对象的参数:

The first takes 0 or more arguments, each an iterable, the second one takes one argument which is expected to produce the iterables:

from itertools import chain

chain(list1, list2, list3)

iterables = [list1, list2, list3]
chain.from_iterable(iterables)

但 iterables 可以是任何产生可迭代对象的迭代器:

but iterables can be any iterator that yields the iterables:

def gen_iterables():
    for i in range(10):
        yield range(i)

itertools.chain.from_iterable(gen_iterables())

使用第二种形式通常是一种方便的情况，但由于它会延迟循环输入可迭代对象，因此它也是链接无限个有限迭代器的唯一方法:

Using the second form is usually a case of convenience, but because it loops over the input iterables lazily, it is also the only way you can chain an infinite number of finite iterators:

def gen_iterables():
    while True:
        for i in range(5, 10):
            yield range(i)

chain.from_iterable(gen_iterables())

上面的例子将给你一个迭代，它产生一个循环的数字模式，它永远不会停止，但永远不会消耗比单个 range() 调用所需更多的内存.

The above example will give you a iterable that yields a cyclic pattern of numbers that will never stop, but will never consume more memory than what a single range() call requires.

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