Python实现迭代器(__next__和__iter__)

一、简单示例

死循环

class Foo:
    def __init__(self, x):
        self.x = x

    def __iter__(self):
        return self

    def __next__(self):
        self.x += 1
        return self.x


f = Foo(3)
for i in f:
    print(i)

二、StopIteration异常版

加上StopIteration异常

class Foo:
    def __init__(self, start, stop):
        self.num = start
        self.stop = stop

    def __iter__(self):
        return self

    def __next__(self):
        if self.num >= self.stop:
            raise StopIteration
        n = self.num
        self.num += 1
        return n


f = Foo(1, 5)

from collections import Iterable, Iterator
print(isinstance(f, Iterator))
#输出
True

for i in Foo(1, 5):
    print(i)

#输出
1
2
3
4

三、模拟range

class Range:
    def __init__(self, n, stop, step):
        self.n = n
        self.stop = stop
        self.step = step

    def __next__(self):
        if self.n >= self.stop:
            raise StopIteration
        x = self.n
        self.n += self.step
        return x

    def __iter__(self):
        return self


for i in Range(1, 7, 3):
    print(i)
#输出
1
4

四、斐波那契数列

class Fib:
    def __init__(self):
        self._a = 0
        self._b = 1

    def __iter__(self):
        return self

    def __next__(self):
        self._a, self._b = self._b, self._a + self._b
        return self._a

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f1 = Fib()

for i in f1:
    if i > 100:
        break
    print('%s ' % i, end='')
#输出
1 1 2 3 5 8 13 21 34 55 89