問(wèn)題描述

我正在研究 Alex Marteli 的 Python 簡(jiǎn)述 并且本書(shū)建議任何具有 next() 方法的對(duì)象都是(或至少可以用作)迭代器.它還表明，大多數(shù)迭代器是通過(guò)對(duì)名為 iter 的方法的隱式或顯式調(diào)用來(lái)構(gòu)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.

讀完這本書(shū)后，我有一種嘗試的沖動(dòng).我啟動(dòng)了一個(gè) python 2.7.3 解釋器并這樣做了:

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()

然而結(jié)果是這樣的:

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

在困惑中，我試圖通過(guò) dir(x) 研究 x 對(duì)象的結(jié)構(gòu)，我注意到它有一個(gè) __iter__ 函數(shù)對(duì)象.所以我發(fā)現(xiàn)它可以用作迭代器，只要它支持那種類(lèi)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.

所以當(dāng)我再次嘗試時(shí)，這次略有不同，嘗試這樣做:

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

>>> _temp_iter = next(x)

我收到了這個(gè)錯(cuò)誤:

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?yàn)樗坪踔С执私涌冢⑶以谝韵律舷挛闹锌隙梢杂米饕粋€(gè):

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

有人可以幫我澄清一下嗎?

推薦答案

它們是可迭代的，但它們不是迭代器.它們可以被傳遞給 iter() 以隱式地(例如通過(guò) for)或顯式地為它們獲取迭代器，但它們本身并不是迭代器.

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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