面向对象-属性查找与绑定方法

2025-02-14 技术教程

1.属性查找

类有两种属性
1.数据属性:类的数据属性是所有对象共享的
2.函数属性:类的函数属性是绑定给对象使用的，称为绑定到对象的方法

#!/usr/bin/env python# -*- coding:utf-8 -*-# Author: vitaclass Student: school = 'my_school' def __init__(self,name,sex,age): self.name=name self.sex=sex self.age=age def learn(self): #函数属性 print('is learning') def eat(self): #函数属性 print('is eating') def sleep(self): print('is sleeping')#"1.类中的数据属性是所有对象共享的，id都一样"s1=Student("vita",'女',27)s2=Student("超超",'男',29)print("id(Student.school)",id(Student.school))print("id(s1.school)",id(s1.school))print("id(s2.school)",id(s2.school))#"类的函数是绑定给对象用的，称为绑定到对象的方法，内存地址都不一样"print("Student.learn",Student.learn)print("s1.learn",s1.learn)print("s2.learn",s2.learn)E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.pyid(Student.school) 1427361290736id(s1.school) 1427361290736id(s2.school) 1427361290736Student.learn <function Student.learn at 0x0000014C555D1D90>s1.learn <bound method Student.learn of <__main__.Student object at 0x0000014C555D85C0>>s2.learn <bound method Student.learn of <__main__.Student object at 0x0000014C555D87F0>>Process finished with exit code 0#对于school变量，会先到s1.__dict__中查找，即先到自己的名称空间中查找# 找不到，去类中查找# 类中找不到，去父类中查找，直到找到顶级父类，找不到，抛出异常#并不会到类的外面查找

"验证变量首先到对象空间中找，然后到类中找，再到父类中找""1.先从对象空间中查找，即s1.__dict__中"#!/usr/bin/env python# -*- coding:utf-8 -*-# Author: vitaschool = 'my_school from out'class Student: def __init__(self,name,sex,age): self.name=name self.sex=sex self.age=ages1=Student("vita",'女',27)s2=Student("超超",'男',29)s1.school="my_school from s1"print(s1.__dict__)print(s1.school)E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py{'name': 'vita', 'sex': '女', 'age': 27, 'school': 'my_school from s1'}my_school from s1Process finished with exit code 0"2.再从类中找"#!/usr/bin/env python# -*- coding:utf-8 -*-# Author: vitaschool = 'my_school from out'class Student: def __init__(self,name,sex,age): self.name=name self.sex=sex self.age=ages1=Student("vita",'女',27)s2=Student("超超",'男',29)Student.school="my_school from class"print(s1.__dict__)print(s1.school)E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.py{'name': 'vita', 'sex': '女', 'age': 27}my_school from classProcess finished with exit code 0"3.再从父类中找，稍后讲继承后，再看""4.类中没有，不会到类外找"#!/usr/bin/env python# -*- coding:utf-8 -*-# Author: vitaschool = 'my_school from out'class Student: def __init__(self,name,sex,age): self.name=name self.sex=sex self.age=ages1=Student("vita",'女',27)s2=Student("超超",'男',29)print(s1.__dict__)print(s1.school)E:\PythonProject\python-test\venvP3\Scripts\python.exe E:/PythonProject/python-test/BasicGrammer/test.pyTraceback (most recent call last):{'name': 'vita', 'sex': '女', 'age': 27} File "E:/PythonProject/python-test/BasicGrammer/test.py", line 15, in <module> print(s1.school)AttributeError: 'Student' object has no attribute 'school'Process finished with exit code 12.绑定方法

类中定义的函数(没有被任何装饰器装饰的)是类的函数属性，主要是给对象使用的，而且是绑定到对象的，虽然所有对象指向的都是相同的功能，但绑定到不同的对象就是不同的绑定方法
因为绑定给哪个对象，就由哪个对象调用，就会把对象自身当做参数传给self，即自动传值（init方法也是生成对象时，自动运行的）
注意：绑定到对象的方法的这种自动传值的特征，决定了在类中定义的函数都要默认写一个self参数，self可以是任意名字，但默认大家都写为self

Python中的数据类型也是一种类，与类的操作是相同的

#list类型是类list>>> list<class 'list'>>>> set<class 'set'>>>> dict<class 'dict'>>>> str<class 'str'>#实例化三个对象>>> l1=list()>>> l2=list()>>> l3=list()#三个对象都有绑定方法append,是相同的功能，但内存地址不同>>> l1.append<built-in method append of list object at 0x0000027FEE617408>>>> l2.append<built-in method append of list object at 0x0000027FEE617448>>>> l3.append<built-in method append of list object at 0x0000027FEE617488>#操作绑定方法l1.append(3)就是往l1添加3,不会影响l2和l3>>> l1.append(3)>>> l1[3]>>> l2[]>>> l3[]#调用类list.append(l3,111)等同于l3.append(111)>>> list.append(l3,111)>>> l3[111]4.面向对象优点小节4.1优点1：将数据与操作数据的功能整合到一起

"1.在没有学习类概念时，数据与功能是分离的"def exc1(host,port,db,charset): conn=connect(host,port,db,charset) conn.execute(sql) return xxxdef exc2(host,port,db,charset,proc_name) conn=connect(host,port,db,charset) conn.call_proc(sql) return xxx#每次调用都需要重复传入一堆参数exc1('127.0.0.1',3306,'db1','utf8','select * from tb1;')exc2('127.0.0.1',3306,'db1','utf8','存储过程的名字')

"2.我们后面用到一个解决办法，即全局变量"HOST=‘127.0.0.1’PORT=3306DB=‘db1’CHARSET=‘utf8’def exc1(host,port,db,charset): conn=connect(host,port,db,charset) conn.execute(sql) return xxxdef exc2(host,port,db,charset,proc_name) conn=connect(host,port,db,charset) conn.call_proc(sql) return xxxexc1(HOST,PORT,DB,CHARSET,'select * from tb1;')exc2(HOST,PORT,DB,CHARSET,'存储过程的名字')

"3.学到类之后，是这样的将数据与专门操作该数据的功能整合到一起"class MySQLHandler: def __init__(self,host,port,db,charset='utf8'): self.host=host self.port=port self.db=db self.charset=charset self.conn=connect(self.host,self.port,self.db,self.charset) def exc1(self,sql): return self.conn.execute(sql) def exc2(self,sql): return self.conn.call_proc(sql)obj=MySQLHandler('127.0.0.1',3306,'db1')obj.exc1('select * from tb1;')obj.exc2('存储过程的名字')4.2优点2：可扩展性高

"定义类并产生三个对象"class Chinese: def __init__(self,name,age,sex): self.name=name self.age=age self.sex=sexp1=Chinese('egon',18,'male')p2=Chinese('alex',38,'female')p3=Chinese('wpq',48,'female')

"如果我们新增一个类属性，将会反映给所有对象，而对象却无需修改，直接使用新增的属性即可"class Chinese: country='China' def __init__(self,name,age,sex): self.name=name self.age=age self.sex=sex def tell_info(self): info=''' 国籍:%s 姓名:%s 年龄:%s 性别:%s ''' %(self.country,self.name,self.age,self.sex) print(info)p1=Chinese('egon',18,'male')p2=Chinese('alex',38,'female')p3=Chinese('wpq',48,'female')print(p1.country)p1.tell_info()