Python __len__()、__reversed__()、__contains__()

1.  
   class A(object):
2.  
   def __init__(self,num):
3.  
   self.num = num
4.  
   self.start_num = -1
5.  
    
6.  
   def __len__(self):
7.  
   ‘‘‘
8.  
   @summary: 当使用len(Test)该对象时调用该方法，当没有该方法是会报错，且返回数据不为整数也会报错
9.  
   ‘‘‘
10.  
    print "__len__"
11.  
    return self.num - self.start_num - 1
12.  
     
13.  
    if __name__ == "__main__":
14.  
    print len(A(10))

1.  
   __len__
2.  
   10

__reversed__():当使用reversed函数翻转对象时调用

1.  
   class A(object):
2.  
   def __init__(self,num):
3.  
   self.num = num
4.  
    
5.  
   def __reversed__(self):
6.  
   ‘‘‘
7.  
   @summary: 当使用reversed函数翻转对象时调用
8.  
   ‘‘‘
9.  
   ret = []
10.  
    for i in range(self.num):
11.  
    ret.append(self.num - i-1)
12.  
    return ret
13.  
     
14.  
    if __name__ == "__main__":
15.  
    print reversed(A(10))

[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]

1.  
   class A(object):
2.  
   def __init__(self,num):
3.  
   self.num = num
4.  
    
5.  
   def __contains__(self, item):
6.  
   ‘‘‘
7.  
   @summary:当使用in，not in 对象的时候 ,not in 是在in完成后再取反,实际上还是in操作
8.  
   ‘‘‘
9.  
   print "__contains__:%s is in?"%item
10.  
    if item < self.num and item >= 0:
11.  
    return True
12.  
    return False
13.  
     
14.  
    if __name__ == "__main__":
15.  
    if 3 in A(10):print "True"
16.  
    else:print False
17.  
    if 3 not in A(10):print "True"
18.  
    else:print False

1.  
   __contains__:3 is in?
2.  
   True
3.  
   __contains__:3 is in?
4.  
   False