Python的内置方法和类的继承举例

Posted 2021-01-25

1.类的内置方法

Python内部类：
所谓内部类，就是在类的内部定义的类，主要目的是为了更好的抽象现实世界。
例子：
汽车是一个类，汽车的底盘轮胎也可以抽象为类，将其定义到汽车内中，而形成内部类，
更好的描述汽车类，因为底盘轮胎是汽车的一部分。
内部类实例化方法：

方法1：直接使用外部类调用内部类
方法2：先对外部类进行实例化，然后再实例化内部类
out_name = outclass_name()
in_name = out_name.inclass_name()
in_name.method()

#!/usr/bin/env python
#-*- coding:utf-8  -*-
class People(object):
    color = ‘yellow‘
    __age = 30   #私有属性

    class Chinese(object):
        print("I am chinese")

    def think(self):
        self.color = "black"
        print "I am a %s "  % self.color
        print ("I am a thinker")
        print self.__age

    def  __talk(self):
        print "I am talking with Tom"

    @classmethod #调用类的方法 
    def test(self):
        print ("this is class method")

    @staticmethod  #调用类的方法 
    def test1():    
        print ("this is static method")

jack = People.Chinese()

#!/usr/bin/env python
#-*- coding:utf-8  -*-
class People(object):
    color = ‘yellow‘
    __age = 30   #私有属性

    class Chinese(object):
        name ="I am a Chinese."

    def think(self):
        self.color = "black"
        print "I am a %s "  % self.color
        print ("I am a thinker")
        print self.__age

    def  __talk(self):
        print "I am talking with Tom"

    @classmethod #调用类的方法 
    def test(self):
        print ("this is class method")

    @staticmethod  #调用类的方法 
    def test1():    
        print ("this is static method")

jack = People.Chinese()  #外部类调用内部类
print jack.name     #外部类调用内部类对象

另一种方法，外部类调用内部类对象

#!/usr/bin/env python
#-*- coding:utf-8  -*-
class People(object):
    color = ‘yellow‘
    __age = 30   #私有属性

    class Chinese(object):
        name ="I am a Chinese."

    def think(self):
        self.color = "black"
        print "I am a %s "  % self.color
        print ("I am a thinker")
        print self.__age

    def  __talk(self):
        print "I am talking with Tom"

    @classmethod #调用类的方法 
    def test(self):
        print ("this is class method")

    @staticmethod  #调用类的方法 
    def test1():    
        print ("this is static method")

ren = People()            #实例化外部类
jack = ren.Chinese()   #实例化内部类
print jack.name           #打印内部类属性

或
print People.Chinese.name
print People.Chinese().name

魔术方法：

str(self)
构造函数与析构函数
构造函数:

用于初始化类的内部状态，Python提供的构造函数是__init__():
__init__():方法是可选的，如果不提供，python会给出一个默认的__init__方法。

析构函数：

用于释放对象占用的资源，python提供的析构函数是__del__():
__del__():也是可选的，如果不提供，则python会在后台提供默认析构函数。

构造函数str

#!/usr/bin/env python
#-*- coding:utf-8  -*-
class People(object):
    color = ‘yellow‘
    __age = 30   #私有属性

    class Chinese(object):
        name ="I am a Chinese."

    def __str__(self):
        return "This is People class"

    def think(self):
        self.color = "black"
        print "I am a %s "  % self.color
        print ("I am a thinker")
        print self.__age

    def  __talk(self):
        print "I am talking with Tom"

    @classmethod #调用类的方法 
    def test(self):
        print ("this is class method")

    @staticmethod  #调用类的方法 
    def test1():    
        print ("this is static method")

ren = People()            #实例化外部类
print ren     #默认执行__str__

init(self)初始化类：

#!/usr/bin/env python
#-*- coding:utf-8  -*-
class People(object):
    color = ‘yellow‘
    __age = 30   #私有属性

    class Chinese(object):
        name ="I am a Chinese."

    def __str__(self):
        return "This is People class"

    def __init__(self,c=‘white‘):   #类实例化时自动执行
        self.color = c
 self.think()

    def think(self):
        self.color = "black"
        print "I am a %s "  % self.color
        print ("I am a thinker")
        print self.__age

    def  __talk(self):
        print "I am talking with Tom"

    @classmethod #调用类的方法 
    def test(self):
        print ("this is class method")

    @staticmethod  #调用类的方法 
    def test1():    
        print ("this is static method")

jack = People(‘green‘)
ren = People()            #实例化外部类
print ren.color        #通过对象访问属性是初始化后的值
print People.color    #通过类访问还是原来的值   

[[email protected] 20180110]# python test1.py 
I am a black 
I am a thinker
30
black
yellow

析构函数del()：释放资源

#!/usr/bin/env python
#-*- coding:utf-8  -*-
class People(object):
    color = ‘yellow‘
    __age = 30   #私有属性

    class Chinese(object):
        name ="I am a Chinese."

    def __str__(self):
        return "This is People class"

    def __init__(self,c=‘white‘):   #类实例化时自动执行
        print ("initing...")
 self.color = c
        self.think()
        f = open(‘test.py‘)

    def think(self):
        self.color = "black"
        print "I am a %s "  % self.color
        print ("I am a thinker")
        print self.__age

    def  __talk(self):
        print "I am talking with Tom"

    @classmethod #调用类的方法 
    def test(self):
        print ("this is class method")

    @staticmethod  #调用类的方法 
    def test1():    
        print ("this is static method")

     def __del__(self):
          print ("del....")
   self.f.close()

jack = People(‘green‘)
ren = People()            #实例化外部类
print ren.color        #通过对象访问属性是初始化后的值
print People.color    #通过类访问还是原来的值   

垃圾回收机制：

Python采用垃圾回收机制来清理不再使用的对象;python提供gc模块释放不再使用的对象。
Python采用“引用计数”的算法方式来处理回收，即：当然某个对象在其作用域内不再被其
他对象引用的时候，python就自动化清除对象。
gc模块collect()可以一次性收集所有待处理的对象(gc.collect)

#!/usr/bin/env python
#-*- coding:utf-8  -*-
class People(object):
    color = ‘yellow‘
    __age = 30   #私有属性

    class Chinese(object):
        name ="I am a Chinese."

    def __str__(self):
        return "This is People class"

    def __init__(self,c=‘white‘):   #类实例化时自动执行
        print ("initing...")
                 self.color = c
        self.think()
        f = open(‘test.py‘)

    def think(self):
        self.color = "black"
        print "I am a %s "  % self.color
        print ("I am a thinker")
        print self.__age

    def  __talk(self):
        print "I am talking with Tom"

    @classmethod #调用类的方法 
    def test(self):
        print ("this is class method")

    @staticmethod  #调用类的方法 
    def test1():    
        print ("this is static method")

     def __del__(self):
          print ("del....")
   self.f.close()

print gc.collect()     如果是0是没有回收的。
jack = People(‘green‘)
ren = People()            #实例化外部类
print ren.color        #通过对象访问属性是初始化后的值
print People.color    #通过类访问还是原来的值   

2.类的继承

类的继承

继承是面向对象的重要特性之一，

继承关系继承是相对两个类而言的父子关系

子类继承了父类的所有公有属性和方法，

继承，实现了代码重用

使用继承

继承可以重用已经存在的数据和行为，减少代码的重复编写,

Python在类名后使用一对括号来表示继承关系，括号中的即类为父类

class Myclass(ParentClass)，

如果父类定义了__init__方法，子类必须显式调用父类的__init__方法，

ParentClass.__init__(self,[args...])

如果子类需要扩展父类的行为，可以添加__init__方法的参数.

#!/usr/bin/env python
#-*- coding:utf-8  -*-
class People(object):
    color = ‘yellow‘

    def think(self):
    self.color = "black"
    print "I am a %s "  % self.color
    print ("I am a thinker")

class Chinese(People):
    pass

cn = Chinese()
print cn.color
cn.think()

父类中有构造函数：

#!/usr/bin/env python
#-*- coding:utf-8  -*-
class People(object):
    color = ‘yellow‘
     def __init__(self):
        print "Init..."
        self.dwell = ‘Earth‘
    def think(self):
        print "I am a %s "  % self.color
        print ("I am a thinker")
class Chinese(People):
    pass
cn = Chinese()
print cn.dwell
cn.think()

参数大于两个：

#!/usr/bin/env python
#-*- coding:utf-8  -*-
class People(object):
    color = ‘yellow‘
    def __init__(self,c):
        print "Init..."
        self.dwell = ‘Earth‘
     def think(self):
        print "I am a %s "  % self.color
        print ("I am a thinker")
class Chinese(People):
     def __init__(self):
        People.__init__(self,‘red‘)
        pass
cn = Chinese()

Super 函数

class A(object):
        def __init__(self):
            print "enter A"
            print "leave A"
class B(object):
        def __init__(self):
            print "enter B"
            super(B,self),__init__()
            print "leave B"
b = B()

#!/usr/bin/env python
#-*- coding:utf-8  -*-
class People(object):
    color = ‘yellow‘
    def __init__(self,c):
        print "Init..."
        self.dwell = ‘Earth‘
    def think(self):
        print "I am a %s "  % self.color
        print ("I am a thinker")
class Chinese(People):
    def __init__(self):
       super(Chinese,self).__init__(‘red‘)
       pass
cn = Chinese()
cn.think()

#!/usr/bin/env python
#-*- coding:utf-8  -*-
class People(object):
    color = ‘yellow‘
    def __init__(self,c):
        print "Init..."
        self.dwell = ‘Earth‘
    def think(self):
        print "I am a %s "  % self.color
        print ("I am a thinker")
class Chinese(People):
    def __init__(self):
        super(Chinese,self).__init__(‘red‘)
     def talk(self):
        print "I like taking."
cn = Chinese()
cn.think()
cn.talk()

多重继承

Python支持多重继承，第一个类可以继承多个父类

语法:

class class_name(Parent_c1,Parent_c2,...)

注意:

当父类中出现多个自定义的__init__的方法时，

多重继承，只执行第一个累的__init_方法，其他不执行。

#!/usr/bin/env python
#-*- coding:utf-8  -*-
class People(object):
    color = ‘yellow‘
    def __init__(self):
        print "Init..."
        self.dwell = ‘Earth‘
    def think(self):
        print "I am a %s "  % self.color
        print ("My home is %s ") % self.dwell
class Martian(object):
    color = ‘red‘
    def __init__(self):
        self.dwell = ‘Martian‘
class Chinese(People,Martian):
    def __init__(self):
        People.__init__(self)
cn = Chinese()
cn.think()

#!/usr/bin/env python
#-*- coding:utf-8  -*-
class People(object):
    def __init__(self):
        self.dwell = ‘Earth‘
         self.color = ‘yellow‘
    def think(self):
        print "I am a %s "  % self.color
        print ("My home is %s ") % self.dwell
class Martian(object):
    color = ‘red‘
    def __init__(self):
        self.dwell = ‘Martian‘
    def talk(self):
        print "I like talking"
class Chinese(Martian,People):
    def __init__(self):
        People.__init__(self)
cn = Chinese()
cn.think()
cn.talk()