python - 从消费者生成器返回单个值

Question

我有一个消费者生成器的管道。我想从最后一个消费者中在某个时间点返回结果。这有效:

class StopIterationWithResult(StopIteration):
    def __init__(self, result):
        super(StopIterationWithResult, self).__init__()
        self.result = result

# for definition fo consumer decorator see http://www.python.org/dev/peps/pep-0342/
@consumer
def waitfor3():
    while True:
        value = (yield)
        if value == 3:
            raise StopIterationWithResult('Hello')

c = waitfor3()
for i in range(10):
    try:
        print 'calling', i
        c.send(i)
    except StopIterationWithResult as r:
        print 'stopped', r.result
        break

还有更好的办法吗？例如，如果生成器由于 return 语句而引发 StopIteration，您能否访问生成器的返回值？

根据@alexis的要求，下面是一个带有管道的示例:

class StopIterationWithResult(StopIteration):
    def __init__(self, result):
        super(StopIterationWithResult, self).__init__()
        self.result = result

@consumer
def add1_filter(consumer):
    while True:
        value = (yield)
        consumer.send(value+1)

@consumer
def waitfor3():
    while True:
        value = (yield)
        print 'got', value
        if value == 3:
            raise StopIterationWithResult('Hello')

c = waitfor3()
f = add1_filter(c)
for i in range(10):
    try:
        print 'calling', i
        f.send(i)
    except StopIterationWithResult as r:
        print 'stopped', r.result
        break

这与 @Martijn Pieters 的答案相同 - 但使过滤器变得更难看:

@consumer
def add1_filter(consumer):
    result = None
    while True:
        value = (yield result)
        result = consumer.send(value+1)

@consumer
def waitfor3():
    while True:
        value = (yield)
        print 'got', value
        if value == 3:
            yield 'Hello'
            break

c = waitfor3()
f = add1_filter(c)
r = None
for i in range(10):
    try:
        print 'calling', i
        r = f.send(i)
    except StopIteration:
        print 'stopped', r
        break

Answer 1

产量是双向的。在右侧表达式中使用时，它将接收并用作语句，它会生成表达式的结果。

只需产生结果值:

def waitfor3():
    while True:
        value = (yield)
        if value == 3:
            yield 'Hello'
            break

c = waitfor3()
for i in range(10):
    try:
        print 'calling', i
        result = c.send(i)
    except StopIteration:
        print 'stopped', result
        break