what does yield as assignment do? myVar = (yield)

Question

I'm familiar with yeild to return a value thanks mostly to this question

but what does yield do when it is on the right side of an assignment?

@coroutine
def protocol(target=None):
   while True:
       c = (yield)

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

I came across this, on the code samples of this blog, while researching state machines and coroutines.

Answer 1

You can send values to the generator using the send function.

If you execute:

p = protocol()
p.next() # advance to the yield statement, otherwise I can't call send
p.send(5)

then yield will return 5, so inside the generator c will be 5.

Also, if you call p.next(), yield will return None.

You can find more information here.

Answer 2

The yield statement used in a function turns that function into a "generator". The resulting iterator is normally resumed by calling next(). However it is possible to send values to the function by calling the method send() instead of next() to resume it:

cr.send(1)

In your example this would assign the value 1 to c each time.

cr.next() is effectively equivalent to cr.send(None)