1 x = 'hello'
2 # print(dir(x))
3 iter_test = x.__iter__()
4 print(iter_test)
5 print(iter_test.__next__())
6 print(iter_test.__next__())
7 print(iter_test.__next__())
8 print(iter_test.__next__())
9 print(iter_test.__next__())

1 li = [1,2,3,4]
2 iter_li = li.__iter__() #遵行可迭代协议，故生成了可迭代对象
3 print(iter_li.__next__())
4 print(iter_li.__next__())

1 li = [1,2,3,4]
2 for i in li:  # 因为li具有__iter__()属性，所以它具有了__next__()的属性，可以进行迭代
3     print(i)          #for 循环具有普遍适用性
4
5 index = 0
6 while index < len(li):    # 这种方法只适用于列表、字符串、元素，这些具有可迭代属性的类型，超出了这些，这种办法就不能用了
7     print(li[index])
8     index+=1

1 1
2 2
3 3
4 4
5 1
6 2
7 3
8 4

1 se = {1,2,3,4,5,6}
2 for i in se:
3     print(i)
4 se_iter = se.__iter__()
5 print(se_iter.__next__())
6 print(se_iter.__next__())
7 print(se_iter.__next__())

1 1
2 2
3 3
4 4
5 5
6 6
7 1
8 2
9 3

1 di = {'a':1,'b':2,'c':3,'d':4}
2 iter_di = di.__iter__()
3 print(iter_di.__next__())
4 print(iter_di.__next__())
5 print(iter_di.__next__())

1 a
2 b
3 c

1 f = open('test.txt','r+',encoding='utf-8')
2 iter_f = f.__iter__()
3 print(iter_f)
4 print(iter_f.__next__(),end='')
5 print(iter_f.__next__(),end='')
6 print(iter_f.__next__(),end='

1 <_io.TextIOWrapper name='test.txt' mode='r+' encoding='utf-8'>
2 12344556
3 abcdef
4 ABCDEFG

1 li = [1,2,3,4,5]
2 diedai_li = li.__iter__()
3
4 while True:
5     try:
6         print(diedai_li.__next__())
7     except StopIteration:
8         print('迭代完成，循环已终止')
9         break

1 1
2 2
3 3
4 4
5 5
6 迭代完成，循环已终止

1 ll = ['爷爷','爸爸','儿子','孙子','重孙']
2 iter_ll = iter(ll)            # ll.__iter__()  等价于  iter(ll)
3 print(iter_ll.__next__())
4 print(next(iter_ll))
5 print(iter_ll.__next__())
6 print(next(iter_ll))

1 爷爷
2 爸爸
3 儿子
4 孙子