Python - playing with send function

send.py

def gen():
    print("running up to yield!")
    while 1:
        # Receiving value from 'send'
        x = yield
        print("Incoming: {}".format(x))
        if x is None:
            print("Exiting")
            break
        doubled = x * 2
        print("Yielding: {}".format(doubled))
        # yielding back doubled value.
        # This value would be used as result of send function
        yield doubled
    yield  # final yield in case if None received

print("Creating generator")
g = gen()
print("Calling next!")
next(g)
print("Sending: 5")
received = g.send(5)
print("Received {}".format(received))

next(g)
print("Sending: 3")
received = g.send(3)
print("Received {}".format(received))

next(g)
print("Sending: 10")
received = g.send(10)
print("Received {}".format(received))

next(g)
print("Sending: None")
received = g.send(None)
print("Received {}".format(received))

# output
"""
Creating generator
Calling next!
running up to yield!
Sending: 5
Incoming: 5
Yielding: 10
Received 10
Sending: 3
Incoming: 3
Yielding: 6
Received 6
Sending: 10
Incoming: 10
Yielding: 20
Received 20
Sending: None
Incoming: None
Exiting
Received None

Process finished with exit code 0
"""