对 python 列表感到困惑:它们是还是不是迭代器?

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?

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