ping_pong.py

pong_c = None
ping_c = None

def ping():
    i = 0
    while True:
        res = yield 
        print(res)
        i += 1
        pong_c.send("ping")
        
def pong():
    i = 0
    while True:
        res = yield
        print(res)
        i += 1
        ping_c.send("pong")

pong_c = pong()
ping_c = ping()

pong_c.send(None)
ping_c.send(None)

ping_c.send("start")