迭代器和可迭代对象

import re
import reprlib

RE_WORD = re.compile('w+')


class SentenceIterator:
    def __init__(self, words):
        self.words = words
        self.index = 0

    def __next__(self):
        try:
            word = self.words[self.index]
        except IndexError:
            raise StopIteration()
        self.index += 1
        return word

    def __iter__(self):
        # 其实可以不用写
        return self


class Sentence:
    def __init__(self, text):
        self.text = text
        self.words = RE_WORD.findall(text)

    def __repr__(self):
        return 'Setence(%s)' % reprlib.repr(self.text)

    def __iter__(self):
        return SentenceIterator(self.words)


s4 = Sentence('pig and pepper')
it = iter(s4)

print(next(it))
print(next(it))
print(next(it))
'''
注意：可迭代对象内部并不实现__next__方法，因为每次调用iter(my_iterable)都需要生成一个新的迭代器
'''