Python运算符重载用法实例分析

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

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

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]

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

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

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__

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. 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__

希望本文所述对大家的Python程序设计有所帮助。

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