为什么可迭代对象不是迭代器? [英] Why is an iterable object not an iterator?

问题描述

这是我的代码:

from collections import deque

class linehistory:
    def __init__(self, lines, histlen=3):
        self.lines = lines
        self.history = deque(maxlen=histlen)

    def __iter__(self):
        for lineno, line in enumerate(self.lines,1):
            self.history.append((lineno, line))
            yield line

    def clear(self):
        self.history.clear()


f = open('somefile.txt')
lines = linehistory(f)
next(lines)

错误:

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

我不知道为什么linehistory对象不是迭代器，因为它已经在the类中包含了__iter__方法.

I have no idea why the linehistory object is not an iterator since it has already included __iter__ method in the class.

推荐答案

迭代的概念已得到充分证明 Python文档中的.

The concept of iteration is well documented in the Python documentation.

简而言之，可迭代"是我要迭代的对象，也称为容器.这可以是列表，字符串，元组或其他任何包含或可以产生多个项目的内容.它具有__iter__()返回迭代器.

In short, "iterable" is the object I want to iterate over, also called the container. This can be a list, a string, a tuple or anything else which consists of or can produce several items. It has __iter__() which returns an iterator.

迭代器"是用于一次迭代的对象.可以将其视为一种光标".它具有next()(在Python 2中)或__next__()(在Python 3中)，被重复调用直到引发StopIteration异常.由于任何迭代器也都是可迭代的(作为其自己的迭代器)，因此它还具有返回其自身的__iter__().

An "iterator" is the object which is used for one iteration. It can be seen as a kind of "cursor". It has next() (in Python 2) or __next__() (in Python 3) which is called repeatedly until it raises a StopIteration exception. As any iterator is iterable as well (being its own iterator), it also has __iter__() which returns itself.

您可以使用iter(obj)获得任何可迭代的迭代器.

You can get an iterator for any iterable with iter(obj).

在您的示例中，linehistory(应写为LineHistory)是可迭代的，因为它具有.__iter__().以此创建的生成器对象是一个迭代器(就像每个生成器对象一样).

In your example, linehistory (which should be written LineHistory) is iterable as it has an .__iter__(). The generator object created with this is an iterator (as every generator object).

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