iterator, yield, send

def foo():
    x = 2
    while True:
        print('a x: {}'.format(x))
        x = yield 2*x
        print('c x: {}'.format(x))

f = foo()
print('begin')
i = next(f)
print('0i: {}'.format(i))
while True:
    try:
        i = f.send(i * 3)
    except StopIteration:
        break
    print('1i: {}'.format(i))
    if i > 10000:
        break