Python运算符重载

2009年08月13日 星期四 06:48 P.M.

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]，
                            For If
__len__        长度            len(X)
__cmp__        比较            X==Y,X__lt__        小于            X__eq__        等于            X=Y
__radd__        Right-Side +        +X
__iadd__        +=                X+=Y
__iter__        迭代            For In
7.1    减法重载

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

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

class indexer:
    def __getitem__(self, index): #iter override
        return index ** 2
X = indexer()
X[2]
for i in range(5):
    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

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

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

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

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

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__

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

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)

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

class Life:
    def __init__(self, name='name'):
        print 'Hello', name
        self.name = name
    def __del__(self):
        print 'Goodby', self.name

brain = Life('Brain') #call __init__
brain = 'loretta'    # call __del__