Python 面向对象之类class和对象基本用法示例
人气:0本文实例讲述了Python 面向对象之类class和对象基本用法。分享给大家供大家参考,具体如下:
类(class):定义一件事物的抽象特点,usually,类定义了事物的属性和它可以做到的性为
对象(object):是类的实例。
1.基本点
class MyClass(object): message = "hello,world" def show(self): print (self.message)
类名为MyClass 有一个成员变量:message,并赋予初值
类中定义了成员函数show(self),注意类中的成员函数必须带有参数self
参数self是对象本身的引用,在成员函数中可以引用self参数获得对象的信息
输出结果:
inst = Myclass() # 实例化一个MyClass 的对象 inst.show # 调用成员函数,无需传入self参数 hello,world
注: 通过在类名后面加小括号可以直接实例化类来获得对象变量,使用对象变量可以访问类的成员函数与成员变量。
2.构造函数
构造函数是一种特殊的类成员方法,主要用来创建对象初始化,python 中的类构造函数用__init__命名:
class MyClass(object): message = 'Hello, Developer.' def show(self): print self.message def __init__(self): print "Constructor is called" inst = MyClass() inst.show() >>>
打印结果:
>>>Constructor is called >>>Hello, Developer.
注:构造函数不能有返回值,python 中不能定义多个构造函数,但可以通过为命名参数提供默认值的方式达到用多种方式构造对象的目的。
3.析构函数
是构造的反向函数,在销毁或者释放对象时调用他们。
python 中为类定义析构函数的方法在类定义中定义一个名为__del__的没有返回值和参数的函数。
class MyClass(object): message = 'Hello, Developer.' def show(self): print self.message def __init__(self, name = "unset", color = "black"): print "Constructor is called with params: ",name, " ", color def __del__(self): print "Destructor is called!" inst = MyClass() inst.show() inst2 = MyClass("David") inst2.show() del inst, inst2 inst3 = MyClass("Lisa", "Yellow") inst3.show() del inst3 >>>
打印结果:
Constructor is called with params: unset black
Hello, Developer.
Constructor is called with params: David black
Hello, Developer.
Destructor is called!
Destructor is called!
Constructor is called with params: Lisa Yellow
Hello, Developer.
Destructor is called!
4.实例成员变量
构造函数中定义self引用的变量,因此这样的成员变量在python中叫做实例成员变量。
def __init__(self, name = "unset", color = "black"): print "Constructor is called with params: ",name, " ", color self.name = name self.color = color
5.静态函数和类函数:
python 支持两种基于类名访问成员的函数:静态函数,类函数。
区别在于:类函数有一个隐形参数cls可以用来获取类信息。而静态函数没有该函数。
静态函数用装饰器:@staticmethod定义
类函数使用装饰器:@classmethod定义
class MyClass(object): message = 'Hello, Developer.' def show(self): print (self.message) print ("Here is %s in %s!" % (self.name, self.color)) @staticmethod def printMessage(): print ("printMessage is called") print (MyClass.message) @classmethod def createObj(cls, name, color): print ("Object will be created: %s(%s, %s)"% (cls.__name__, name, color)) return cls(name, color) def __init__(self, name = "unset", color = "black"): print ("Constructor is called with params: ",name, " ", color) self.name = name self.color = color def __del__(self): print ("Destructor is called for %s!"% self.name) MyClass.printMessage() inst = MyClass.createObj( "Toby", "Red") print (inst.message) del inst
输出结果:
printMessage is called
Hello, Developer.
Object will be created: MyClass(Toby, Red)
Constructor is called with params: Toby Red
Hello, Developer.
Destructor is called for Toby!
6.私有成员
python 使用指定变量名格式的方法定义私有成员,即所有以双下划线“__”开始命名的成员都为私有成员。
class MyClass(object): def __init__(self, name = "unset", color = "black"): print "Constructor is called with params: ",name, " ", color self.__name = name self.__color = color def __del__(self): print "Destructor is called for %s!"% self.__name inst = MyClass("Jojo", "White") del inst
输出结果:
Constructor is called with params: Jojo White
Destructor is called for Jojo!
注明:书《Python 高效开发实战Django, Tornado, Flask, Twisted》总结
希望本文所述对大家Python程序设计有所帮助。
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