python基础--面向对象

 一、建立对象

'''
在类的内部，使用 def 关键字来定义一个方法，与通常函数定义不一样，
类方法必须包含参数 self, 且为第一个参数，self 表明的是类的实例。
''' 

#!/usr/bin/python3
#类定义
class People:
    #定义基本属性
    name = ''
    age = 0
    #定义私有属性,私有属性在类外部没法直接进行访问
    __weight = 0
    
    #定义构造方法
    def __init__(self,name,age,weight):
        self.name = name
        self.age = age
        self.__weight = weight
        
    #定义普通方法
    def speak(self):
        print("name=%s, age=%d" %(self.name, self.age))
        
    def __str__(self):
        return "name=%s, age=%d" %(self.name, self.age)

 
# 实例化类
p = People('tom', 10, 30)
p.speak()
print("name=%s, age=%d" %(p.name, p.age))
print("*" * 10)
print(p)

 

二、__del__方法

import sys
class MyClass:
    def __del__(self):
        print("执行__del__方法。。。")
 
# 实例化类
x1 = MyClass()
x2 = x1

# 查询对象的引用个数
print("引用个数：", sys.getrefcount(x1))
print("引用个数：", sys.getrefcount(x2))

del x1
print("*" * 20)
del x2 #对象的引用计数为0时调用__del__方法
print("*" * 20)

 

三、类属性和实例属性

#类定义
class People:
    #定义基本属性
    name = ''
    age = 0
    #定义私有属性,私有属性在类外部没法直接进行访问
    __weight = 0
    
    #定义构造方法
    def __init__(self,name,age,weight):
        self.name = name
        self.age = age
        self.__weight = weight
        
    #定义普通方法
    def speak(self):
        print("name=%s, age=%d" %(self.name, self.age))
        
    def __str__(self):
        return "name=%s, age=%d" %(self.name, self.age)

 
# 实例化类, 并访问实例属性的值
p = People('tom', 10, 30)
p.speak()
print("name=%s, age=%d" %(p.name, p.age))
print("*" * 10)
print(p)

# 访问类属性的值
print("name=%s, age=%d" %(People.name, People.age))

 

四、类方法、实例方法、静态方法

class People:
    #定义基本属性
    name = ''
    
    def __init__(self, name):
        self.name = name
    
    #实例方法
    def printName(self):
        print(self.name)
        
    #类方法
    @classmethod
    def setName(cls, name):
        cls.name = name
        
    #静态方法
    @staticmethod
    def sayHi():
        print("hello world")
 

People.setName("tom")
print(People.name)
People.sayHi()
print("*" * 20)

# 类方法与静态方法也能够经过对象类调用
p = People("jack")
p.printName()
p.setName("haha")
print(People.name)
p.sayHi()

 

五、__new__方法

class People(object):
    name = ""
    def __init__(self, name):
        self.name = name
        print("init...")
    
    def __del__(self):
        print("del...")
        
    def __new__(cls, name):
        print("new...")
        return object.__new__(cls)
    
p = People("tom")
print(p.name)

 

六、单例

class People(object):
    __instance = None
    
    def __new__(cls):
        if cls.__instance == None:
            cls.__instance = object.__new__(cls)
        return cls.__instance

p1 = People()
print(id(p1))

p2 = People()
print(id(p2))

　　__init__方法调用了屡次

class People(object):
    __instance = None
    
    def __new__(cls, name):
        if cls.__instance == None:
            cls.__instance = object.__new__(cls)
        return cls.__instance
    def __init__(self, name):
        self.name = name
        
p1 = People("tom")
print(id(p1))
print(p1.name) #tom

p2 = People("jack")
print(id(p2))
print(p2.name) #jack

 

　　只初始化一次

class People(object):
    __instance = None
    __flag = False
    
    def __new__(cls, name):
        if cls.__instance == None:
            cls.__instance = object.__new__(cls)
        return cls.__instance
    def __init__(self, name):
        if People.__flag == False:
            self.name = name
            People.__flag = True
        
p1 = People("tom")
print(id(p1))
print(p1.name)

p2 = People("jack")
print(id(p2))
print(p2.name)