包含yield的語句的函數可作爲生成器對象用next(iterator)或__next__()調用(兩個下劃線),yield代表此處返回一個值並暫停後面語句
def f(it):
while True:
for i in it:
yield i
f=f(['a','b','c'])
print("next(iterator)調用:")
for i in range(10):
print(next(f))
print("__next__()調用",f.__next__(),sep=":")