neat.py

def cool():
    n = 0
    while True:
        delta = yield n
        if delta is not None:
            n += delta
        else:
            n += 1


# Used like an iterator
it = cool()
print(it.send(None))
print(it.send(None))
print(it.send(None))
print(it.send(None))
print(it.send(None))

# You can pass a delta in to say how much you wan to increment
coro = cool()
print(coro.send(None))
print(coro.send(2))
print(coro.send(1))
print(coro.send(5))
print(coro.send(1))

output

0
1
2
3
4
--------------------------------------------------------------------------------
0
2
3
8
9