小弟正在學習PYTHON，看到generator時，下面這支是看得懂...
gen.send.preparation.stop.py
stop = False
def counter(start=0):
n = start
while not stop:
yield n
n += 1
c = counter()
print(next(c)) # prints: 0
print(next(c)) # prints: 1
stop = True
print(next(c)) # raises StopIteration
不過到了下面這支後就卡關了...
我卡關的點在於... 為什麼執行# C步驟時，只有印出0；
而執行# D時卻是印出：
<class 'str'> Wow!
1
為什麼不是先印出1呢? 明明result = yield n 就是在前面啊...
如果按照這邏輯的話，步驟# F應該也要先印出3才對...
可是卻先執行# B 印出<class 'str'> Q 後產生StopIteration
麻煩各位大大賜教了，感謝!!
gen.send.py
def counter(start=0):
n = start
while True:
result = yield n # A
print(type(result), result) # B
if result == 'Q':
break
n += 1
c = counter()
print(next(c)) # C
print(c.send('Wow!')) # D
print(next(c)) # E
print(c.send('Q')) # F
執行結果：
$ python gen.send.py
0
<class 'str'> Wow!
1
<class 'NoneType'> None
2
<class 'str'> Q
Traceback (most recent call last):
File "gen.send.py", line 14, in <module>
print(c.send('Q')) # F
StopIteration

C->A->C(0)->D->A->B(Wow)->A->D(1)->....another example: https://goo.gl/5VVhSZ

next(g) == g.send(None)yield 右邊的值會先出來，左值會在下次 send 的時候 assign& 這個其實是 coroutine 了，見 PEP342