创建迭代器

>>> class TestIter():
 def __init__(self,lst):
  self.lst = lst

 # 重写可迭代协议__iter__
 def __iter__(self):
  print('__iter__ is called')
  return iter(self.lst)

# =========================  
# 迭代 TestIter 类：
# =========================
>>> t = TestIter()
>>> t = TestIter([1,3,5,7,9])
>>> for e in t:
 print(e)


__iter__ is called
1
3
5
7
9