Python生成器的经典程序

import random

def get_data():
    """返回0到9之间的3个随机数"""
    return random.sample(range(10), 3)

def consume():
    """显示每次传入的整数列表的动态平均值"""
    running_sum = 0
    data_items_seen = 0

    while True:
        data = yield
        data_items_seen += len(data)
        running_sum += sum(data)
        print('The running average is {}'.format(running_sum / float(data_items_seen)))

def produce(consumer):
    """产生序列集合，传递给消费函数（consumer）"""
    while True:
        data = get_data()
        print('Produced {}'.format(data))
        consumer.send(data)
        yield

if __name__ == '__main__':
    consumer = consume()#启动生成器
    consumer.send(None)
    producer = produce(consumer)

    for _ in range(10):
        print('Producing...')
        next(producer)

对比：yield作为语句还是表达式。

import random

def get_data():
    """返回0到9之间的3个随机数"""
    return random.sample(range(10), 3)

def consume(data):
    """显示每次传入的整数列表的动态平均值"""
    running_sum = 0
    data_items_seen = 0

    while True:
        data = yield data
        """内部挂起生成器，yield作为表达式而不是语句"""
        """生成器运行时，yield返回一个值，就是外部通过send方法发送的值"""
        data_items_seen += len(data)
        running_sum += sum(data)
        print('The running average is {}'.format(running_sum / float(data_items_seen)))

def produce(consumer):
    """产生序列集合，传递给消费函数（consumer）"""
    while True:
        data = get_data()
        print('Produced {}'.format(data))
        consumer.send(data)
        yield

if __name__ == '__main__':
    consumer = consume(0)
    consumer.send(None)
    producer = produce(consumer)

    for _ in range(10):
        print('Producing...')
        next(producer)