Python：协程 - StopIteration 异常

Question

我正在尝试使用 .send() 来提供字典。我的代码片段如下

def coroutine(func):
    def start(*args, **kwargs):
        cr = func(*args, **kwargs)
        next(cr)
        return cr
    return start

@coroutine
def putd(di):

    print("via coroutines adding a key : value to dictionary")

    try:
        item = yield
        for key, value in item.items():
            if key in di:
                print("Key : {0} already exists".format(key))
            else:
                di[key] = value
        print(di)
    except StopIteration :
        print("yield frame got closed")


di = {}
gobj = putd(di)
gobj.send({"plan" : "shuttle"})
gobj.close()

而且我相信我正在正确处理 exception 但我仍然遇到 StopIteration 异常。

scratch.py
Traceback (most recent call last):
via coroutines adding a key : value to dictionary
{'plan': 'shuttle'}
File "scratch.py", line 39, in <module>
    gobj.send({"plan" : "shuttle"})
StopIteration

Process finished with exit code 1

我是不是没有正确处理该异常，还是遗漏了什么？非常感谢任何帮助。

Answer 1

您的协程在第一个 send/yield 后退出。这会生成一个 StopIteration 并且您不能在协程本身中处理它，但只能在调用 send 时处理它。来自文档：

The send() method returns the next value yielded by the generator, or raises StopIteration if the generator exits without yielding another value.

@coroutine
def putd(di):

    print("via coroutines adding a key : value to dictionary")

    try:
        item = yield
        for key, value in item.items():
            if key in di:
                print("Key : {0} already exists".format(key))
            else:
                di[key] = value
        print(di)
    except StopIteration :
        print("yield frame got closed")
    # here is an implicit  return None  which terminates the coroutine

我猜你想让协程保持活动状态，接受尽可能多的发送，直到显式 close:

@coroutine
def putd(di):

    print("via coroutines adding a key : value to dictionary")

    try:
        while True:
            item = yield
            for key, value in item.items():
                if key in di: 
                    print("Key : {0} already exists".format(key))
                else:
                    di[key] = value
            print(di)
    except GeneratorExit:
        print("yield frame got closed")

请注意，现在捕获了 GeneratorExit 异常。

Python：协程 - StopIteration 异常

Python: Coroutines - StopIteration exception

python

python-3.x

generator

coroutine

stopiteration