Python 类的魔术方法

>>>

>>> 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

>>>