python __cmp__ 重載

ideal_gjh

1. >>>  class  Dog:
   
2. ...         def  __cmp__(self,other):
   
3. ... if  other  >  0  :  return  1;
   
4. ... elif  other  <  0  :  return  -1;
   
5. ... else:  return  0
   
6. ...
   
7. >>>  dog  =  Dog()
   
8. >>>  if  dog  >  -10  :  print  "ok"
   
9. ...
   
10. >>>  if  dog  <  -10  :  print  "ok"
    
11. ...
    
12. ok
    
13. >>>  if  dog  ==  0  :  print  "ok"
    
14. ...
    
15. ok
    
16. >>>

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這個(gè)代碼一直沒(méi)有理解，有人詳細(xì)解釋下嗎，3q.

laike9m

拿dog和數(shù)字比較的意義何在？

Perl_Er

回復(fù) 1# ideal_gjh


    這個(gè)例子是哪里來(lái)的啊，給你看個(gè)例子：http://www.tutorialspoint.com/python/python_classes_objects.htm

1. Overloading Operators:
   
2. Suppose you've created a Vector class to represent two-dimensional vectors. What happens when you use the plus operator to add them? Most likely Python will yell at you.
   
3. 
   
4. You could, however, define the __add__ method in your class to perform vector addition, and then the plus operator would behave as per expectation:
   
5. 
   
6. EXAMPLE:
   
7. #!/usr/bin/python
   
8. 
   
9. class Vector:
   
10.    def __init__(self, a, b):
    
11.       self.a = a
    
12.       self.b = b
    
13. 
    
14.    def __str__(self):
    
15.       return 'Vector (%d, %d)' % (self.a, self.b)
    
16.    
    
17.    def __add__(self,other):
    
18.       return Vector(self.a + other.a, self.b + other.b)
    
19. 
    
20. v1 = Vector(2,10)
    
21. v2 = Vector(5,-2)
    
22. print v1 + v2
    
23. When the above code is executed, it produces following result:
    
24. 
    
25. Vector(7,8)

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