协程

Generators as Coroutines

How Coroutines Evolved from Generators

Coroutines(协程) via Enhanced Generators was implemented in Python 2.5, and add .send method to generator objects.

Using .send(), the caller of the generator can post data that then becomes the value of the yield expression inside the generator function. This allows a generator to be used as a coroutine: a procedure that collaborates with the caller, yielding and receving values from the caller. A coroutine can be in one of four states. You can determine the current state using the inspect.getgeneratorstate(..) function, which returns one of these strings:

• GEN_CREATED: waiting to start execution.
• GEN_RUNNING: currently being executed by the interpreter
• GEN_SUSPENDED: currently suspended at a yield expression
• GEN_CLOSED: execution has completed.

GEN_CREATED
-> Started: a= 10
10
GEN_SUSPENDED
-> Received: b= 28
38
-> Received: c= 99
StopIteration
GEN_CLOSED

Execution of the simple_coro2 coroutine can be split in three phases:

1. next(my_coro2) prints first message and runs to yield a, yielding number 14.
2. my_coro2.send(28) assigns 28 to b, prints second message, and runs to yield a + b, yielding number 42.
3. my_coro2.send(99) assigns 99 to c, prints third message, and the coroutine terminates. The Example below uses coroutine to compute a running average.

Coroutine Termination and Exception Handling