【语法16】Python面向对象1

定义与使用类

类的定义

class testClass:
    name = "Xu Huan"
    def welcome(self):
        print("Xu Huan is handsome")

xu = testClass()
print(xu.name)
xu.welcome()

Xu Huan
Xu Huan is handsome

Python要求类的方法的第一个参数必须是self，表示的是实例本身。

class testClass:
    name = "Xu Huan"
    def welcome(self):
        print("实例：",self)
        print("类：",self.__class__)

xu = testClass()
print(xu.name)
xu.welcome()

Xu Huan
实例： <__main__.testClass object at 0x0000015D2B529208>
类： <class '__main__.testClass'>

self是推荐写法，写成别的也可以。

class testClass:
    name = "Xu Huan"
    def welcome(this):
        print("实例：",this)
        print("类：",this.__class__)

xu = testClass()
print(xu.name)
xu.welcome()

Xu Huan
实例： <__main__.testClass object at 0x0000015D2B529D68>
类： <class '__main__.testClass'>

类的构造方法和析构方法

构造方法：实例化类时自动执行的方法，定义时用__init__形式。

析构方法：销毁类时自动执行的方法，定义时用__del__形式。

class MacketMember:
    def __init__(self):
        print("welcome")
    def __del__(self):
        pass
    
m = MacketMember()

welcome

类的私有属性

类的私有属性，对象无法调用，只有类内部才可以使用。

class MarketMember:
    __count = 0
    __name = ''
    def __init__(self,name,count):
        self.__count += count
        self.__name = name
    def seek(self):
        print(self.__name + "积分为" + str(self.__count))
        
m = MarketMember('Xu Huan',300)
m.seek()
print(m.__count)  #无法输出私有属性__count

Xu Huan积分为300



---------------------------------------------------------------------------

AttributeError                            Traceback (most recent call last)

<ipython-input-11-6e059803e4af> in <module>()
     10 m = MarketMember('Xu Huan',300)
     11 m.seek()
---> 12 print(m.__count)  #无法输出私有属性__count


AttributeError: 'MarketMember' object has no attribute '__count'

类的私有方法

类的私有方法和私有属性一样，也是以双下划线__开始，不能被对象调用。

class MarketMember:
    def __change(self,count):
        print("修改后的分数是" + str(count))
    
m = MarketMember()
m.__change(500)

---------------------------------------------------------------------------

AttributeError                            Traceback (most recent call last)

<ipython-input-13-caf5b4253243> in <module>()
      4 
      5 m = MarketMember()
----> 6 m.__change(500)


AttributeError: 'MarketMember' object has no attribute '__change'

一个完整的类

class MarketMember:
    __name = ""
    count = 600
    def __init__(self,name):
        self.__name = name
        print(self.__name + '当前积分：' + str(self.count))
    def change(self,count1):
        self.count += count1
        print(self.__name + '更改后的积分为：' + str(self.count))
        
m = MarketMember('Xu Huan')
m.change(500)
print(m.count)

Xu Huan当前积分：600
Xu Huan更改后的积分为：1100
1100

类与类的关系

单继承

class MarketMember:
    __name = ""  #私有属性无法被继承的类使用
    count = 600
    def __init__(self,name):
        self.__name = name
        print(self.__name + '当前积分：' + str(self.count))
    def change(self,count1):
        self.count += count1
        print(self.__name + '更改后的积分为：' + str(self.count))
        
class MyMember(MarketMember):
    age = 0
    def seekAge(self):
        print("年龄为：" + str(self.age) + "，积分为：" + str(self.count))
        
m = MyMember('Xu Huan')
m.change(500)
m.age = 25
m.seekAge()

Xu Huan当前积分：600
Xu Huan更改后的积分为：1100
年龄为：25，积分为：1100

多继承

class Animals:
    color = ""
    weight = 0
    def jump(self):
        print('i can jump')
        
class cat:
    def miaomiao(self):
        print('i can miaomiao')

class whitecat(Animals,cat):
    def white(self):
        print('i am white')
        
w = whitecat()
w.jump()
w.miaomiao()
w.white()

i can jump
i can miaomiao
i am white

类的关联和依赖

依赖

Person类的方法gobyboat需要boat作为参数传入，这样才能调用boat的过河(overriver)方法，这就叫依赖。

class Person:
    def gobyboat(self,boat):
        boat.overriver()
    
class Boat:
    def overriver(self):
        print("go successfully!")

b = Boat()
p = Person()
p.gobyboat(b)

go successfully!

关联

class empluee:
    id = 0
    name = ''
    
class Company:
    def __init__(self):
        self.employee = employee()

重写

Python允许子类重写父类中已有的方法，而且不需要特殊的关键字进行说明。

class Animals:
    color = ""
    weight = 0
    def jump(self):
        print('i can jump')
        
class cat:
    def miaomiao(self):
        print('i can miaomiao')

class whitecat(Animals,cat):
    def miaomiao(self):
        print('i can white miaomiao')
    def white(self):
        print('i am white')
        
w = whitecat()
w.jump()
w.miaomiao()
w.white()

i can jump
i can white miaomiao
i am white

魔术方法

魔术方法能够给类增加魔力，如果对我们的对象实现（重载）了这些方法中的某一个，那么这个方法就会在特殊的情况下被Python自动调用。

#__call__方法是允许一个类的实例像函数一样被调用。
class Person:
    def __init__(self,name,age):
        self.name = name
        self.age = age
    def __call__(self,*args):
        print(str(args[0] + args[1]))
        
p = Person('Xu Huan',22)
p(150,250)

400

#__getitem__、__setitem__是获取键或设置键，一般用于类中的一些自定义数据结构。
class Person:
    def __init__(self,name,age):
        self.name = name
        self.age = age
        self._registry = {
            'name' : name,
            'age' : age
        }
    def __getitem__(self,key):
        if key not in self._registry.keys():
            raise Exception('please registry the key: %s first!' % (key,))
        return self._registry[key]
    def __setitem__(self,key,value):
        if key not in self._registry.keys():
            raise Exception('please registry the key: %s first!' % (key,))
        self._registry[key] = value
        
p = Person('Xu Huan',22)
print(p['name'],p['age'])
p['age'] = 23
print(p['age'])

Xu Huan 22
23

#__get__、__set__，如果类的某个属性设置了描述符，对这个类的访问会触发特定的绑定行为。
class Meter:
    def __init__(self,value = 0.0):
        self.value = float(value)
    def __get__(self,instance,owner):
        return self.value
    def __set__(self,instance,value):
        self.value = float(value)
        
class Foot:
    def __get__(self,instance,owner):
        return instance.meter * 3.2808
    def __set__(self,instance,value):
        instance.meter = float(value) / 3.2808
        
class Distance:
    meter = Meter()
    foot = Foot()

d = Distance()
print(d.meter,d.foot)
d.meter = 1
print(d.meter,d.foot)
d.meter = 2
print(d.meter,d.foot)

0.0 0.0
1.0 3.2808
2.0 6.5616