魔术方法：迭代器

迭代说人话就是循环
iter():iter()
next():next()

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>>> str = "asdfsadf"
>>> it = iter(str)
>>> next(it)
'a'
>>> next(it)
's'
>>> next(it)
'd'
>>> while True:
	try :
		each = next(it)
	except StopIteration:
		break
	print(each)

	
f
s
a
d
f
```  

e.g. 
self.a,self.b   =   self.b,self.a+self.b 可以理解成：
temp_1 = self.b
temp_2 = self.a + self.b

self.a = temp_1
self.b = temp_2

斐波那契数列：

class fibs:
def init(self):
self.a = 0
self.b = 1
def iter(self):
return self
def next(self):
self.a,self.b = self.b,self.a+self.b
return self.a

f = fibs()
for each in f:
if each < 50:
print(each)
else:
break

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34

1

改良：

class fibs:
def init(self,n=50):
self.a = 0
self.b = 1
self.n = n
def iter(self):
return self
def next(self):
self.a,self.b = self.b,self.a+self.b
if self.a > self.n:
raise StopIteration
return self.a

f = fibs()
for each in f:
print(each)

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34

f = fibs(100)
for each in f:
print(each)

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34
55
89
`