Python:使用`yield from`时出现奇怪的行为 [英] Python: Weird behavior while using `yield from`

问题描述

在下面的代码中，我遇到了RecursionError: maximum recursion depth exceeded.

In the following code, I have run into a RecursionError: maximum recursion depth exceeded.

def unpack(given):
    for i in given:
        if hasattr(i, '__iter__'):
            yield from unpack(i)
        else:
            yield i

some_list = ['a', ['b', 'c'], 'd']

unpacked = list(unpack(some_list))

如果我使用some_list = [1, [2, [3]]]，这很好用，但是当我尝试使用字符串时，效果不佳.

This works fine if I use some_list = [1, [2, [3]]], but not when I try it with strings.

我怀疑我对python的了解不足.任何指导表示赞赏.

I suspect my lack of knowledge in python. Any guidance appreciated.

推荐答案

字符串是无限可迭代的.甚至一个字符的字符串也是可迭代的.

Strings are infinitely iterable. Even a one-character string is iterable.

因此，除非为字符串添加特殊处理，否则始终会出现堆栈溢出:

Therefore, you will always get a stack overflow unless you add special handling for strings:

def flatten(x):
    try:
        it = iter(x)
    except TypeError:
        yield x
        return
    if isinstance(x, (str,  bytes)):
        yield x
        return
    for elem in it:
        yield from flatten(elem)

注意:使用hasattr(i, '__iter__')不足以检查i是否可迭代，因为还有其他方法可以满足迭代器协议. 仅一种可靠的方法来确定是否可迭代的对象是调用iter(obj).

Note: using hasattr(i, '__iter__') is not sufficient to check if i is iterable, because there are other ways to satisfy the iterator protocol. The only reliable way to determine whether an object is iterable is to call iter(obj).

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