python 基础——运算符重载

方法	重载	调用
__init__	构造函数	x = Class()
__del__	析构函数	del x
__str__	打印	print x
__call__	调用函数	x(*args)
__getattr__	获取属性	y = x.method
__setattr__	设置属性	x.any = value
__getitem__	获取索引	x[key]
__setitem__	设置新索引	x[key] = value
__len__	长度	len(x)
__iter__	迭代	for item in x:
__add__	加	x + y
__sub__	减	x - y
__mul__	乘	x * y
__radd__
__iadd__	左加 +=	x += y
__or__	或 |	x | y
__cmp__	比较 ==	x == y
__lt__	小于 <	x < y
__eq__	等于 =	x = y

减法重载

重载"-" 不同对象的减法处理

class Number:
    def __init__(self,start):
        self.data=start
    def __sub__(self,other):
         return Number(self.data-other)
number=Number(20)
y=number-10
print number.data, y.data

重载"-" 相同对象的减法处理

class Big :
     def __init__(self,a,b):
         self.a=a
         self.b=b
     def __sub__(self,other):#other不用事先制定类型,可以直接当做一个Big来用
        return Big(self.a-other.a,self.b-other.b)
i=Big(20,12);
j=Big(23,4);
k=i-j;
print k.a ,k.b

重载"+"

class AddOperator :
     def __init__(self,a,b):
         self.a=a
         self.b=b
     def __add__(self,other):#other不用事先制定类型,可以直接当做一个Big来用
        return Big(self.a+other.a,self.b+other.b)
i=AddOperator(20,12);
j=AddOperator(23,4);
k=i+j;
print k.a ,k.b

重载"+="

class AddOperator :
     def __init__(self,a,b):
         self.a=a
         self.b=b
     def __iadd__(self,other):#other不用事先制定类型,可以直接当做一个Big来用
        return Big(self.a+other.a,self.b+other.b)
i=AddOperator(20,12);
j=AddOperator(23,4);
i+=j;
print i.a ,i.b

重载乘法

不同对象的乘法：

class MulOperator:
    def __init__(self,a,b):
        self.a=a
        self.b=b
    def __mul__(self,n):
        return MulOperator(self.a*n,self.b*n)
i=MulOperator(20,5)
j=i*4.5
print j.a,j.b

索引重载

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 __setitem__(self, key,value): #iter override
          self.mydict[key] = value
        return self.mydict
X = indexer()  

X[2] = 'test'    # 它等于调用 X.__setitem__(2, 'test') 

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(%d)"% self.data    # %d ,%s都可以
x=addrepr(2)
x+1
print x ,repr(x)
i=3;
print "%s---%d"% (i, i)

调用重载

__call__相当与 X()

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)

析构重载 __del__

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__

重载"|"

class Mat :
    def __init__(self,value):
       self.age=value
    def __or__(self,other):
        return self.age!=0 and other.age!=0
a=Mat(10)
b=Mat(21)
c=Mat(0)
print a|b ,a|c

打印转换重载

class PrintOperator:
    def __init__(self,a):
        self.a=a
    def __str__(self,b=50):
       return "I am %s years old!" % self.a
i=PrintOperator(10)
print i, str(i)

长度重载

class lenOperator:
    def __init__(self,a,b,c):
         (self.a,self.b,self.c)=(a,b,c)
    def __len__(self):
        return 3
a=lenOperator(0,2,4)
print len(a)

cmp重载

class cmpOperator:
    def __init__(self,a,b,c):
        (self.a,self.b,self.c)=(a,b,c)
    def __cmp__(self,other):
        if self.a>other.a:
           return 1
        elif self.a<other.a:
           return -1
        elif self.b>other.b:
           return 1
        elif self.b<other.b:
            return -1
        elif self.c>self.c:
            return 1
        elif self.c<self.c:
            return -1
        elif self.c==self.c:
           return 0
i=cmpOperator(1,2,3)
j=cmpOperator(2,4,5)
k=cmpOperator(2,4,5)
a=cmpOperator(1,4,5)
print cmp(i,j),cmp(j,k),cmp(a,i)

delattr重载

class delattrOperator(object):
     def __init__(self,a,b):
        (self.a,self.b)=(a,b)
     def __delattr__(self,name):
        print "del obj.%s" % name
        object.__delattr__(self,name)
a=delattrOperator(1,2)
print a.a,a.b
del a.a
print a.b
# print a.a 打印a会出错，a已经被删除。

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