使用 Python 协程时如何避免额外的迭代？

Question

这是 Python 3.9 中的协程

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


@coroutine
def grep(pattern):
    while True:
        line = yield "I have to yield something here?"
        if pattern in line:
            # do something fancy to the line
            yield line
        else:
            raise ValueError("err")

由于line = yield 正在接收和发送数据，我需要进行额外的next 调用才能使其工作：

gg = grep("thing")

item = gg.send("That thing!")
print(item)
next(gg)

item = gg.send("That thing also!")
print(item)
next(gg)

item = gg.send("And what about here this thing.")
print(item)
next(gg)

item = gg.send("Not this.")
print(item)
next(gg)

哪个打印：

That thing!
That thing also!
And what about here this thing.
Traceback (most recent call last):
  File "/home/erasmose/Workspace/clustr/cmapper/temp.py", line 33, in <module>
    item = gg.send("Not this.")
  File "/home/erasmose/Workspace/clustr/cmapper/temp.py", line 16, in grep
    raise ValueError("err")
ValueError: err

如果我删除“下一个”调用：

gg = grep("thing")

item = gg.send("That thing!")
print(item)

item = gg.send("That thing also!")
print(item)

item = gg.send("And what about here this thing.")
print(item)

item = gg.send("Not this.")
print(item)

输出是：

That thing!
I have to yield something here?
And what about here this thing.
I have to yield something here?

有什么方法可以避免那些额外的“下一个”调用？

Answer 1

您需要合并两个yield 语句，以便协程在同一个yield 中发送和接收

不过，您仍然需要额外的收益来启动该过程。

类似这样的：

@coroutine
def grep(pattern):
    line = yield "I have to yield something here?"  # receive the first one
    while True:
        if pattern in line:
            line = yield line  # send and receive in one yield statement
        else:
            raise ValueError("err")