首次使用后 zip 变量为空

2022-01-10 00:00:00 python python-3.x iterator

问题描述

Python 3.2

t = (1, 2, 3)
t2 = (5, 6, 7)
z = zip(t, t2)

for x in z:
    print(x)

结果:

(1, 5)
(2, 6)
(3, 7)

之后立即放入完全相同的循环，什么都不会打印:

Putting in EXACTLY the same loop immediately after, nothing is printed:

for x in z:
    print(x)

z 仍然作为 <zip 对象存在于 0xa8d48ec>.我什至可以重新分配 t、t2 以再次压缩，但它只能工作一次，而且只能工作一次.

z still exists as <zip object at 0xa8d48ec>. I can even reassign the t, t2 to be zipped again, but then it only works once and only once, again.

这是它应该如何工作的吗?文档中没有提及这一点.

Is this how its supposed to work? There's no mention in the docs about this.

解决方案

这就是它在 python 3.x 中的工作方式.在 python2.x 中，zip 返回一个元组列表，但对于 python3.x，zip 的行为类似于 itertools.izip 在 python2.x 中的行为.要恢复 python2.x 的行为，只需从 zip 的输出中构造一个列表:

That's how it works in python 3.x. In python2.x, zip returned a list of tuples, but for python3.x, zip behaves like itertools.izip behaved in python2.x. To regain the python2.x behavior, just construct a list from zip's output:

z = list(zip(t,t2))

请注意，在 python3.x 中，许多内置函数现在返回迭代器而不是列表(map、zip、filter)

Note that in python3.x, a lot of the builtin functions now return iterators rather than lists (map, zip, filter)

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