兼容Python2和Python3的迭代器

除了内置的迭代器类型,任何一个含有__iter__函数、next(Python2)或者__next__函数的类都是迭代器类型。__iter__函数返回一个可迭代的对象;next(Python2)或者__next__函数返回下一个值。

例如,编写一个整数迭代器,从1迭代到100。

Python2

# coding=utf8

class IntegerIterator:
    def __init__(self):
        self._num = 0

    def __iter__(self):
        return self

    def next(self):
        if self._num == 100:
            raise StopIteration
        self._num += 1
        return self._num

if __name__ == '__main__':
    for a in IntegerIterator():
        print(a)

Python3

# coding=utf8

class IntegerIterator:
    def __init__(self):
        self._num = 0

    def __iter__(self):
        return self

    def __next__(self):
        if self._num == 100:
            raise StopIteration
        self._num += 1
        return self._num

if __name__ == '__main__':
    for a in IntegerIterator():
        print(a)

和Python2相比,next函数变成了__next__函数。

兼容Python2和Python3的迭代器

要编写兼容Python2和Python3的迭代器,就很简单:

# coding=utf8

class IntegerIterator:
    def __init__(self):
        self._num = 0

    def __iter__(self):
        return self

    def __next__(self):
        if self._num == 100:
            raise StopIteration
        self._num += 1
        return self._num

    next = __next__


if __name__ == '__main__':
    for a in IntegerIterator():
        print(a)

定义__next__函数,再定义next指向__next__。这样的代码就不会报错误:

# Python2
TypeError: instance has no next() method
# Python3
TypeError: iter() returned non-iterator of type '***'

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