Python学习day23-面向对象的编程

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Python学习day23-面向对象的编程面向过程和面向对象类与对象定义类和对象实例化类对象产生对象属性查找顺序一切皆对象

Python学习day23-面向对象的编程

面向过程和面向对象

我们之前曾经了解过面向过程的一些方法，面向过程的核心也就是过程，过程就是解决问题的步骤，也就是我们将编程流程化，一步一步完成项目，设计一个流水线，面向过程的主要应用场景是一些一旦完成基本不会改变的场景，比如Linux内核，git等等，使用面向过程非常的方便，效率也很高。

面向过程的编程优点是可以将复杂的问题流程化，进而将其简单化，而其缺点也非常明显，我们都明白，工厂里的流水线的话，一旦中间某个环节出了问题，后面的环节都会出问题，且对其改造将会非常麻烦，官方来说就是程序的可扩展性会非常的差，所以我们引入面向对象的编程。

顾名思义，面向对象的编程的核心就在于对象二字，其思想非常的灵活，是以每一个对象为主体，每个对象都是属性和方法的集合体。夸张点说，每个对象都是我们创建的一个世界，我们所要做的就是在这个世界里增增减减，为其创造一切。面向对象所使用的的场景是经常需要变化的软件，一般这些变化都会集中在用户层，所以互联网应用，企业内部的软件以及各种游戏等，都是需要用到面向对象的思想的地方。

说了这么多，面向对象的编程所解决的就是程序的扩展性，对某一个对象单独修改的话，会直接反映到整个体系中，其扩展性非常好，非常的方便。当然其缺点也是很明显的，实现同一个功能，面向对象所使用的代码比面向过程要多出很多，而且面向对象的编程不能很准确的去预测程序的结果，因为其结果大多是不同对象之间相互作用的结果，所以结果不可控因素比较多，容易出现一些非代码性的bug。

类与对象

定义类和对象

类，也可以说是类型，实际上我们之前所用的type查看数据种类，也可以用在这里，看到的就是对象是哪个类里面实例化出来的。

而对象就是属性和方法，也可以说是函数的集合体，但不是必须的，并不是说对象里一定要有属性，有方法，这种思想会让面向对象的编程变得非常的复杂且冗余。

实例化

在现实世界中，我们是先存在一个个具体存在的对象，然后才会有分类的概念，但是Python中是相反的，Python中我们要先定义类，然后通过调用类来生成对象，这个过程就叫做实例化。

类

定义类的方法，就是通过关键字class+函数名（）：

现在我们就来尝试定义一个类

 

 

 

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# 首先定义类名，建议驼峰体命名，约定俗成的事情，没有什么特别的

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# class 关键字，类名

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class Student:  

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 # 变量来表示属性

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 school = 'oldboy'

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    print('我在定义一个类')

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 def choose(self):

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 print('选课...')

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​

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 def study(self):

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 print('学习...')

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# 这里我们就生成了一个类，名为Student，需要注意的几点是：

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# 1. 类中可以有任意的python代码，这些在函数定义以外的代码在类定义的时候就会执行，并不是调用的时候才执行，函数内部的代码则是调用的时候才会执行。

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# 2. 定义类的时候会产生新的名称空间，用来存放类的变量名与函数名，可以通过.__dict__来查看

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​

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# 程序当中类的一些用法：

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print(Student.school)# 即取出school的值

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Student.school = 'xxx'# 为类中的变量赋值

 

 

这里有一些类的特殊属性，这些都是Python为类内置的特殊属性，可以作为了解和扩展。

 

 

 

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.__name__# 类的名字，字符串形式

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.__doc__# 类的文档字符串

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.__base__# 类的第一个父类

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.__basses__# 类的所有父类构成的元组

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.__dict__# 类的字典属性

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.__module__# 类定义所在的模块 

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.__class__ # 实例对应的类

 

 

对象

 

 

 

xxxxxxxxxx

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# 生成对象(类加括号，生成对象）

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stu1 = Student()

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# 获取属性和方法,直接通过.来获取

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print(stu1.school)

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# 对象调用方法，第一个self参数不用传参

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print(stu1.choose)

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stu2 = Student()

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print(stu2.school)

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# 查看类中的属性和方法

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print(Student.__dict__['school'])

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Student.__dict__['choose'](123)# 通过类名直接调用其内部函数的话需要传参给全部的参数，而不是像对象调用方法一样，第一个self形参不必传参，因为对象调用方法的时候会把自己作为第一个self的实参传进去。

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Student.choose(111)

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​

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# 向对象中放属性

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# 上面是第一种方式

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# 第二种，通过__init__在类里面定义对象的属性，其优点是可以在类定义阶段定制属性，为实例化对象提供多样性

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class Student:  # ()

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 # 变量来表示属性

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 school = 'oldboy'

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​

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 # 注意定义名字不要写错，ini之后再tab，不能in直接tab

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 def __init__(self, name):

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 self.name = name

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​

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 def choose(self):

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 print('选课...')

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​

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 def study(self):

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 print('学习...')

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​

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# 产生对象

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stu1 = Student('nick')

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# 当实例化产生对象时会自动调用__init__方法，来完成对象的初始化

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print(stu1.name)

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stu2 = Student('jason')

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print(stu2.name)

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stu1 = Student('nick')

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Student.__init__(stu1,'nick')

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print(stu1.name)

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​

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# 从以上例子我们可以看出，在调用类的时候发生了两件事：

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# 1. 首先创建一个空对象

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# 2. 自动触发类中__init__功能的执行，将stu1以及后面括号内的参数一并传入

 

 

产生对象

属性查找顺序

 

 

 

xxxxxxxxxx

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# 对象自己的属性和方法

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stu1 = Student()

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stu1.name = 'ltd'

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stu1.school = 'xxx'

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print(stu1.__dict__)

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print(stu1.school)

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​

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# 属性查找顺序：

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# 1. 先从对象自身找-->所属类中找-->报错

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​

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Student.school = 'xxxx'

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stu2 = Student()

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print(stu2.school)

 

 

一切皆对象

一句话，Python中一切皆对象。