Python运算符重载

在Python语言中提供了类似于C++的运算符重在功能:
一下为Python运算符重在调用的方法如下:
Method        Overloads        Call for
__init__        构造函数        X=Class()
__del__        析构函数        对象销毁
__add__        +                X+Y,X+=Y
__or__        |                X|Y,X|=Y
__repr__        打印转换        print X,repr(X)
__str__        打印转换        print X,str(X)
__call__        调用函数        X()
__getattr_    限制            X.undefine
__setattr__    取值            X.any=value
__getitem__    索引            X[key],
                            
__len__        长度            len(X)
__cmp__        比较            X==Y,X<Y
__lt__        小于            X<Y
__eq__        等于            X=Y
__radd__        Right-Side +        +X
__iadd__        +=                X+=Y
__iter__        迭代            For In
7.1    减法重载

Python代码
  1. class Number:   
  2.     def __init__(self, start):   
  3.         self.data = start   
  4.     def __sub__(self, other): #minus method   
  5.         return Number(self.data - other)   
  6.   
  7. number = Number(20)   
  8. y = number – 10 # invoke __sub__ method  
class Number:
    def __init__(self, start):
        self.data = start
    def __sub__(self, other): #minus method
        return Number(self.data - other)

number = Number(20)
y = number – 10 # invoke __sub__ method



7.2    迭代重载

Python代码
  1. class indexer:   
  2.     def __getitem__(self, index): #iter override   
  3.         return index ** 2  
  4. X = indexer()   
  5. X[2]   
  6. for i in range(5):   
  7.     print X[i]  
class indexer:
    def __getitem__(self, index): #iter override
        return index ** 2
X = indexer()
X[2]
for i in range(5):
    print X[i]


7.3    索引重载

Python代码
  1. class stepper:   
  2.     def __getitem__(self, i):   
  3.         return self.data[i]   
  4.       
  5. X = stepper()   
  6. X.data = 'Spam'  
  7. X[1] #call __getitem__   
  8.   
  9. for item in X: #call __getitem__   
  10.     print item  
class stepper:
    def __getitem__(self, i):
        return self.data[i]
   
X = stepper()
X.data = 'Spam'
X[1] #call __getitem__

for item in X: #call __getitem__
     print item

 

7.4    getAttr/setAttr重载

Python代码
  1. class empty:   
  2.     def __getattr__(self,attrname):   
  3.         if attrname == 'age':   
  4.             return 40  
  5.         else:   
  6.             raise AttributeError,attrname   
  7. X = empty()   
  8. print X.age #call__getattr__   
  9.   
  10. class accesscontrol:   
  11.     def __setattr__(self, attr, value):   
  12.         if attr == 'age':   
  13.             # Self.attrname = value loops!   
  14.             self.__dict__[attr] = value   
  15.         else:   
  16.             print attr   
  17.             raise AttributeError, attr + 'not allowed'  
  18.   
  19. X = accesscontrol()   
  20. X.age = 40      #call __setattr__   
  21. X.name = 'wang' #raise exception  
class empty:
    def __getattr__(self,attrname):
        if attrname == 'age':
            return 40
        else:
            raise AttributeError,attrname
X = empty()
print X.age #call__getattr__

class accesscontrol:
    def __setattr__(self, attr, value):
        if attr == 'age':
            # Self.attrname = value loops!
            self.__dict__[attr] = value
        else:
            print attr
            raise AttributeError, attr + 'not allowed'

X = accesscontrol()
X.age = 40      #call __setattr__
X.name = 'wang' #raise exception


7.5    打印重载

Python代码
  1. class adder:   
  2.     def __init__(self, value=0):   
  3.         self.data = value   
  4.     def __add__(self, other):   
  5.         self.data += other   
  6.   
  7. class addrepr(adder):   
  8.     def __repr__(self):   
  9.         return 'addrepr(%s)' % self.data   
  10.       
  11. x = addrepr(2)  #run __init__   
  12. x + 1       #run __add__   
  13. print x     #run __repr__  
class adder:
    def __init__(self, value=0):
        self.data = value
    def __add__(self, other):
        self.data += other

class addrepr(adder):
    def __repr__(self):
        return 'addrepr(%s)' % self.data
   
x = addrepr(2)  #run __init__
x + 1       #run __add__
print x     #run __repr__


7.6    Call调用函数重载

Python代码
  1. class Prod:   
  2.     def __init__(self, value):   
  3.         self.value = value   
  4.     def __call__(self, other):   
  5.         return self.value * other   
  6.   
  7. p = Prod(2) #call __init__   
  8. print p(1) #call __call__   
  9. print p(2)  
class Prod:
    def __init__(self, value):
        self.value = value
    def __call__(self, other):
        return self.value * other

p = Prod(2) #call __init__
print p(1) #call __call__
print p(2)



7.7    析构函数重载

Python代码
  1. class Life:   
  2.     def __init__(self, name='name'):   
  3.         print 'Hello', name   
  4.         self.name = name   
  5.     def __del__(self):   
  6.         print 'Goodby', self.name   
  7.   
  8. brain = Life('Brain') #call __init__   
  9. brain = 'loretta'    # call __del__  

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