Python 生成器与迭代器详解

迭代器协议

实现 __iter__() 和 __next__() 方法的对象。

class Counter:

    def __init__(self, limit):

        self.limit = limit

        self.current = 0

    def __iter__(self):

        return self

    def __next__(self):

        if self.current < self.limit:

            self.current += 1

            return self.current

        raise StopIteration



for i in Counter(3):

    print(i)  # 1,2,3

生成器（yield）

生成器是更简单的迭代器实现。

def fibonacci(n):

    a, b = 0, 1

    for _ in range(n):

        yield a

        a, b = b, a + b



for num in fibonacci(5):

    print(num)  # 0,1,1,2,3

生成器表达式

squares = (x**2 for x in range(10))  # 惰性求值

print(next(squares))  # 0

协程 (yield 接收值)

def averager():

    total = 0

    count = 0

    avg = None

    while True:

        value = yield avg

        if value is None:

            break

        total += value

        count += 1

        avg = total / count



coro = averager()

next(coro)  # 启动

print(coro.send(10))  # 10

print(coro.send(20))  # 15

生成器节省内存，适合处理大数据流，也是 asyncio 的核心基础。