>>>
>>> class A:
    def __repr__(self):
        return ‘__repr__‘
     
>>> a = A()
>>> a
__repr__

>>>
>>> class C:
    def __bool__(self):
        return False
     
>>> c = C()
>>> bool(c)
False
>>>

>>> class A:
    def __getattr__(self,name):
        print(‘__getattr__‘)
    def __setattr__(self,name,value):
        print(‘__setattr__‘)
        super().__setattr__(name,value)
    def __delattr__(self,name):
        print(‘__delattr__‘)
        return super().__delattr__(name)
    def __getattribute__(self,name):
        print(‘__getattribute__‘)
        return super().__getattribute__(name)
 
     
>>> a = A()
>>> a.name
__getattribute__         
__getattr__
>>> a.name = ‘daxin‘
__setattr__
>>> a.name
__getattribute__
‘daxin‘
>>> del a.name
__delattr__
>>>

>>> class A:
    def __getattr__(self,name):
        print(‘__getattr__‘)
    def __setattr__(self,name,value):
        print(‘__setattr__‘)
        self.__dict__[name] = value
    def __delattr__(self,name):
        print(‘__delattr__‘)
        return super().__delattr__(name)
    def __getattribute__(self,name):
        print(‘__getattribute__‘)
        return super().__getattribute__(name)
 
 
>>> a = A()
>>> a.name
__getattribute__
__getattr__
>>> a.name = ‘daxin‘
__setattr__
__getattribute__
>>> a.name
__getattribute__
‘daxin‘
>>>

 # 当作一个描述符被访问的含义就是：
 # 一个函数在实例化的时候调用了其他类的对象
  
 >>>
 >>> class A:
      pass
  
 >>> class B:
      def __init__(self):
         self.name = A()     # 把A类的对象在B实例化的时候当作描述符(属性)进行赋值
     
 >>> 

>>> class A:
    def __get__(self,instance,owner):
        print(‘__get__‘,‘self:‘,self,‘instance:‘,instance,‘owner:‘,owner)
     
    def __set__(self,instance,value):
        print(‘__set__‘,‘self:‘,self,‘instance:‘,instance,‘value:‘,value)
 
    def __delete__(self,instance):
        print(‘__delete__‘,‘self:‘,self,‘instance:‘,instance)
 
>>> class B:
    name = A()
 
>>>
>>> b = B()
>>> b.name
__get__ self: <__main__.A object at 0x1134247f0> instance: <__main__.B object at 0x113411d68> owner: <class ‘__main__.B‘>
>>> b.name = ‘abc‘
__set__ self: <__main__.A object at 0x1134247f0> instance: <__main__.B object at 0x113411d68> value: abc
>>> del b.name
__delete__ self: <__main__.A object at 0x1134247f0> instance: <__main__.B object at 0x113411d68>
>>>

class Myproperty:   # 定义自己的Property
 
    def __init__(self,mget=None,mset=None,mdel=None):   # 绑定三个修改方法
        self.mget = mget
        self.mset = mset
        self.mdel = mdel
 
    def __get__(self,instance,owner):
        return self.mget(instance)       
 
    def __set__(self,instance,value):
        return self.mset(instance,value)
 
    def __delete__(self,instance):
        return self.mdel(instance)
 
     
class A:
    def __init__(self):
        self._x = None
 
    def setX(self,value):
        self._x = value
 
    def getX(self):
        try:
            if self._x:
                return self._x
        except AttributeError as e:
            print(‘Attribute is not exist‘)
 
    def delX(self):
        del self._x
 
    name = Myproperty(getX,setX,delX)
   
 
>>> a = A()
>>> a.name
>>> a.name = ‘daxin‘
>>> a.name
‘daxin‘
>>> del a.name
>>> a.name
Attribute is not exist
>>>

>>> class A(int):
    def __add__(self,other):
        print(‘__add__‘)
        return super().__sub__(other)     # 这里改写了 add方法，调用了父类的减法
 
>>> a = A(8)
>>> a + 6
__add__
2
>>>

>>> class A:
    pass
 
>>> class B(int):
 
    def __radd__(self,other):
        return ‘I am B,because right object not have __add__‘
 
     
>>>
>>> a = A()
>>> b = B(12)
>>> a + b
‘I am B,because right object not have __add__‘
>>>

# 定义一个不可变的列表类型
# 记录元素被访问的次数
 
class Mylist:
 
    def __init__(self,*args):
        self.value = [ x for x in args ]    # 列表生成式
        self.count = {}.fromkeys(range(len(self.value)),0)    # 定义字典用于按照索引统计访问次数
 
    def __getitem__(self,key):
        self.count[key] += 1
        return self.value[key]
 
    def __repr__(self):
        return str(self.value)
 
    __str__ = __repr__
 
    
>>> a = Mylist(1,2,3,45)
>>> a
[1, 2, 3，45]
>>> a.count
{0: 0, 1: 0, 2: 0, 3: 0}
>>> a[0]
1
>>> a.count
{0: 1, 1: 0, 2: 0, 3: 0}
>>> a[2]
3
>>> a.count
{0: 1, 1: 0, 2: 1, 3: 0}
>>> a[1] = 123

class Rectangle(object):
 
    # init object
    def __init__(self,width,height):
        self.width = width
        self.height = height
 
 
    def getacreage(self):
        return self.width * self.height
 
    def __setattr__(self,name,value):
        if name == ‘square‘:
            self.width = value
            self.height = value
 
        else:
            super().__setattr__(name,value)
            

import time
 
class Mytimer():
 
    # 初始化
    def __init__(self):
        self.prompt = ‘Timer is not start‘    # 提示信息
        self.start_time = None  
        self.stop_time = None
     
    # 启动定时器
    def start(self):
        if self.start_time:
            print(‘Please Use Stop() to stop Timer‘)   # 属性存在，表示已经启动计时
        else:
            self.start_time = time.time()
            print(‘The start of Timer‘)
 
    # 关闭定时器
    def stop(self):
        if self.start_time:
            self.stop_time = time.time()
            print(‘The stop of Timer‘)
            self._calc()
        else:
         print(‘Please Use Start() to start Timer‘)   # 没有执行start()，检测不到属性，进行提示
 
    # 计算耗时
    def _calc(self):
        self.prompt = ‘Total time : ‘
        self.end_time = self.stop_time - self.start_time
        self.prompt += str(‘{:.2f}‘.format(self.end_time))
        self.start_time = None
        self.stop_time = None
 
    # 直接执行对象时，打印提示信息
    def __repr__(self):
        return self.prompt
 
    # 打印对象和执行对象相同
    __str__ = __repr__
 
    # 计时器相加
    def __add__(self,other):
        self.prompt = ‘All Time : ‘
        add_time = self.end_time + other.end_time
        self.prompt += str(‘{:.2f}‘.format(add_time))
        return self.prompt

class Celsius:
 
    def __init__(self,value = 37):
        self.value = value
 
    def __set__(self,instance,value):
        self.value = value
 
    def __get__(self,instance,owner):
        return self.value
 
 
class Fahrenheit:
 
    def __set__(self,instance,value):
         instance.cel = (float(value) - 32 )  / 1.8
          
    def __get__(self,instance,owner):
        return instance.cel * 1.8  + 32   # 通过instance实例访问，实例化后对象的cel属性
 
class Temperature:
    cel = Celsius()
    fah = Fahrenheit()
 
     
>>> a = Temperature()
>>> a.cel
37
>>> a.fah
98.60000000000001
>>> a.fah = 100
>>> a.cel
37.77777777777778
>>>