Python写一个对象，让它自己能够迭代

仿写range()对象，对象是可迭代的：

 1 #!usr/bin/env python3
 2 # -*- coding=utf-8 -*-
 3 
 4 class myRange():
 5     #初始化,也叫构造函数
 6     def __init__(self,n):
 7         self.i = 0
 8         self.n = n
 9 
10     #类中核心,返回了迭代器本身;
11     def __iter__(self):
12         return self
13 
14     #迭代器开始
15     def __next__(self):
16         if self.i < self.n:
17             i = self.i
18             self.i += 1
19             return i
20         else:
21             raise StopIteration();
22 print(dir(myRange(10)));
23 a = myRange(10);
24 print(dir(a)); #输出:['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__next__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'i', 'n']
25 
26 if __name__ == "__main__":
27     a = myRange(10)
28     print("a=========>", next(a)); #0
29     print("next a====>", next(a)); #1
30     print("next a====>", next(a)); #2
31     print("next a====>", next(a)); #3
32     print("next a====>", next(a)); #4
33     print("next a====>", next(a)); #5
34     print("next a====>", next(a)); #6
35     print("next a====>", next(a)); #7
36     print("next a====>", next(a)); #8
37     print("next a====>", next(a)); #9
38     print("next a====>", next(a)); #发起raise StopIteraion()
39

上面是用next()把迭代器的所有元素一个一个依次打印出来的，当然也可以用for循环循环出来. for i in x: print(i)，然后再用next(a)就会发起raise StopIteration()。下面用列表尝试一下：

 1 #!usr/bin/env python3
 2 # -*- coding=utf-8 -*-
 3 
 4 class myRange():
 5     #初始化,也叫构造函数
 6     def __init__(self,n):
 7         self.i = 0
 8         self.n = n
 9 
10     #类中核心,返回了迭代器本身;
11     def __iter__(self):
12         return self
13 
14     #迭代器开始
15     def __next__(self):
16         if self.i < self.n:
17             i = self.i
18             self.i += 1
19             return i
20         else:
21             raise StopIteration();
22 print(dir(myRange(10)));
23 a = myRange(10);
24 print(dir(a)); #输出:['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__iter__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__next__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'i', 'n']
25 
26 if __name__ == "__main__":
27     b = myRange(10)
28     print(list(b)) #全部打印出来了,后续没有元素了
29     print("b===>next b", next(b)) #StopIteration.

把迭代器里的所有元素装到列表中后，再调用next()也会发起：raise StopIteraion.