Python协程一点理解

yield

def test():
    for i in 'abc':
        yield i
    for i in [1, 2, 3]:
        yield i


if __name__ == '__main__':
    gen = test()
    print(gen.send(None))
    print(gen.send(None))
    print(gen.send(None))
    print(gen.send(None))
    print(gen.send(None))
    print(gen.send(None))
    print(gen.send(None))

def test():
    for i in 'abc':
        yield i
    for i in [1, 2, 3]:
        yield i


if __name__ == '__main__':
    gen = test()
    for i in gen:
        print(i)

使用for循环生成器，因为for循环可以捕捉StopIteration异常。

yield from

上面的代码也可以用yield from实现

def test():
    yield from 'abc'
    yield from [1, 2, 3]


if __name__ == '__main__':
    gen = test()
    for i in test():
        print(i)

yield from 后面需要加的是可迭代对象，它可以是普通的可迭代对象，也可以是迭代器，甚至是生成器。

使用yield from实现实时计算器

def average_gen():
    """
    子生成器
    """
    average = 0
    total = 0
    count = 0
    while True:
        num = yield average
        if num is None:
            break
        count += 1
        total += num
        average = total / count
    return average, count, total


def proxy_gen():
    """
    委派生成器
    """
    while True:
        average, count, total = yield from average_gen()
        print(f'平均值{average}, 计算{count}次, 总和{total}')


def client():
    """
    调用端
    """
    calc_average = proxy_gen()
    calc_average.send(None)
    # next(calc_average)
    # 预激活协程
    print(calc_average.send(10))
    print(calc_average.send(20))
    print(calc_average.send(30))
    calc_average.send(None)
    # 关闭协程


if __name__ == '__main__':
    client()

在委派生成器中的while True可以替换成for循环，循环的大小决定调用端可以calc_average.send(None)的次数(第一次预激活也计入)。

while True和for循环用来捕捉StopIteration异常，可以查看第一段代码。

示例

def average_gen():
    """
    子生成器
    """
    average = 0
    total = 0
    count = 0
    while True:
        num = yield average
        if num is None:
            break
        count += 1
        total += num
        average = total / count
    return average, count, total


def proxy_gen():
    """
    委派生成器
    """
    for i in range(2):
        average, count, total = yield from average_gen()
        print(f'平均值{average}, 计算{count}次, 总和{total}')


def client():
    """
    调用端
    """
    calc_average = proxy_gen()
    calc_average.send(None)
    # next(calc_average)
    # 预激活协程
    print(calc_average.send(10))
    print(calc_average.send(20))
    print(calc_average.send(30))
    calc_average.send(None)
    # 关闭协程
    print(calc_average.send(10))
    print(calc_average.send(20))
    print(calc_average.send(30))
    calc_average.send(None)


if __name__ == '__main__':
    client()

示例最后会抛出StopIteration异常。

因为在第二次calc_average.send(None)时，for循环捕捉了一次异常，进入了最后一次循环，在calc_average.send(None)时，for不能再次循环，不能处理StopIteration异常，故抛出。