Python--30 迭代器

迭代器

　　通常我们接触的迭代器 序列(列表 元组 字符串) 字典

　　通常使用for语句来进行迭代

Python提供了两个BIF

　　iter()

　　__iter__()

　　next()

　　__next__()

>>> for i in ‘Junjie‘:
...     print(i)
...
J
u
n
j
i
e

>>> for item in links:
...     print(‘%s -> %s‘ % (item,links[item]))
...
百度 -> www.baidu.com
谷歌 -> www.google.com
技术 -> stackoverflow

>>> string = ‘junjie‘
>>> it = iter(string)
>>> next(it)
‘j‘
>>> next(it)
‘u‘
>>> next(it)
‘n‘
>>> next(it)
‘j‘
>>> next(it)
‘i‘
>>> next(it)
‘e‘
>>> next(it)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration

>>> string = ‘junjie‘
>>> it = iter(string)
>>> while True:
...     try:
...             each = next(it)
...     except StopIteration:
...             break
...     print(each)
...
j
u
n
j
i
e

>>> for each in string:
...     print(each)
...
j
u
n
j
i
e

魔法方法

>>> 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
...
>>> for each in fibs:
...     if each < 20:
...             print(each)
...     else:
...             break
...
1
1
2
3
5
8
13

>>> class Fibs:
...     def __init__(self,n=10):
...             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
... >>> fibs = Fibs()
>>> for each in fibs:
...     print(each)
...
1
1
2
3
5
8