yield_from.py

# =========================

def ff():
	for i in range(4):
		a = yield i
		print('a:', a)


def gg():
	yield from ff()


def hh():
	yield from gg()


f = hh()
print(f.send(None))
print(f.send(9))
print(f.send(8))

# ff == gg == hh

# =========================

def xx():
    # l = yield from sub_coro()
    # equals to ==>
    s = sub_coro()
    v = None
    while True:
        try:
            t = s.send(v)
            v = yield t
        except StopIteration as e:
            l = e.value
            break