对 python 列表感到困惑:它们是还是不是迭代器?

2022-01-10 00:00:00 python list iterator

问题描述

我正在研究 Alex Marteli 的 Python 简述 并且本书建议任何具有 next() 方法的对象都是(或至少可以用作)迭代器.它还表明，大多数迭代器是通过对名为 iter 的方法的隐式或显式调用来构建的.

I am studying Alex Marteli's Python in a Nutshell and the book suggests that any object that has a next() method is (or at least can be used as) an iterator. It also suggests that most iterators are built by implicit or explicit calls to a method called iter.

读完这本书后，我有一种尝试的冲动.我启动了一个 python 2.7.3 解释器并这样做了:

After reading this in the book, I felt the urge to try it. I fired up a python 2.7.3 interpreter and did this:

>>> x = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> for number in range(0, 10):
...     print x.next()

然而结果是这样的:

Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
AttributeError: 'list' object has no attribute 'next'

在困惑中，我试图通过 dir(x) 研究 x 对象的结构，我注意到它有一个 __iter__ 函数对象.所以我发现它可以用作迭代器，只要它支持那种类型的接口.

In confusion, I tried to study the structure of the x object via dir(x) and I noticed that it had a __iter__ function object. So I figured out that it can be used as an iterator, so long as it supports that type of interface.

所以当我再次尝试时，这次略有不同，尝试这样做:

So when I tried again, this time slightly differently, attempting to do this:

>>> _temp_iter = next(x)

我收到了这个错误:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: list object is not an iterator

但是列表怎么可能不是迭代器，因为它似乎支持此接口，并且在以下上下文中肯定可以用作一个:

But how can a list NOT be an iterator, since it appears to support this interface, and can be certainly used as one in the following context:

>>> for number in x:
...     print x

有人可以帮我澄清一下吗?

解决方案

它们是可迭代的，但它们不是迭代器.它们可以被传递给 iter() 以隐式地(例如通过 for)或显式地为它们获取迭代器，但它们本身并不是迭代器.

They are iterable, but they are not iterators. They can be passed to iter() to get an iterator for them either implicitly (e.g. via for) or explicitly, but they are not iterators in and of themselves.

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