一、内置函数的补充
isinstance(obj,cls)检查是否obj是否是类 cls 的对象
class Foo: pass obj=Foo() print(isinstance(obj,Foo)) # 推荐使用该函数来判断一个函数的类型，判断obj（对象）是否是Foo(类)的对象，是则为真，否则为假 也可用下面main方法判断 print（type(obj) is Foo）
issubclass(sub, super)检查sub类是否是 super 类的派生类
class Foo(object): 2 pass 3 4 class Bar(Foo): 5 pass 6 7 issubclass(Bar, Foo)
二、反射
#下述四个函数是专门用来操作类与对象属性的，如何操作？
#通过字符串来操作类与对象的属性，这种操作称为反射
class People: country="China" def __init__(self,name): self.name=name def tell(self): print('%s is aaa' %self.name) obj=People('egon') # 1、hasattr #判断object中有没有一个name字符串对应的方法或属性 # print(hasattr(People,'country')) #判断类中有没有一个 'country' 字符串对应的方法或属性 # print('country' in People.__dict__) #判断country是否在类的字典中 # print(People.__dict__) #拿到类的字典 # print(hasattr(obj,'name')) # print(hasattr(obj,'country')) #判断obj(对象)有没有一个 'country' 字符串对应的方法或属性 # print(hasattr(obj,'tell')) # 2、getattr # x=getattr(People,'country') #获取类中country的属性是China # x=getattr(People,'country1',None) #获取country1的属性，没有则返回None # print(x) # f=getattr(obj,'tell',None)#obj.tell #获取obj(对象)中tell的函数属性，没有则返回None # print(f == obj.tell) #True # f() # obj.tell() #与f()调用结果相等 # 3、setattr #设置属性 # People.x=111 # setattr(People,'x',111) # print(People.x) # obj.age=18 # setattr(obj,"age",18) # print(obj.__dict__) # 4、delattr #删除属性 # del People.country # delattr(People,"country") # print(People.__dict__) # del obj.name # delattr(obj,"name") # print(obj.__dict__) class Foo: def run(self): while True: cmd=input('cmd>>: ').strip() # print('%s run...' %cmd) if hasattr(self,cmd): #查看属性,用户输入的字符串是download或upload程序才会获得该属性，否则重复循环输入 func=getattr(self,cmd) #获取属性 func() def download(self): print('download....') def upload(self): print('upload...') obj=Foo() obj.run()
三、__str__ 方法
class People: def __init__(self,name,age,sex): self.name=name self.age=age self.sex=sex def __str__(self): #改变对象的字符串显示，如果要把一个类的实例变成 str，就需要实现特殊方法__str__()： # print('========>') #__str__()用于显示给用户 return '<名字：%s 年龄：%s 性别：%s>' %(self.name,self.age,self.sex) obj=People('egon',18,'male') print(obj) #print(obj.__str__()) # l=list([1,2,3]) # print(l)
四、__del__ 方法
import time # # class People: # def __init__(self,name,age,sex): # self.name=name # self.age=age # self.sex=sex # # def __del__(self): # 在对象被删除的条件下，自动执行，没有被删除时不会执行 # print('__del__') # # # obj=People('egon',18,'male') # time.sleep(5) #通过延迟后删除属性，可以看到__del__,才会自动执行 # del obj #obj.__del__() # class Mysql: # def __init__(self,ip,port): # self.ip=ip # self.port=port # self.conn=connect(ip,port) # 申请系统资源 # # def __del__(self): # # self.conn.close() # # obj=Mysql('1.1.1.1',3306) class MyOpen: def __init__(self,filepath,mode="r",encoding="utf-8"): self.filepath=filepath self.mode=mode self.encoding=encoding self.fobj=open(filepath,mode=mode,encoding=encoding) def __str__(self): #定义一个字符串并将其值返回 msg=""" filepath:%s mode:%s encoding:%s """ %(self.filepath,self.mode,self.encoding) return msg def __del__(self): self.fobj.close() f=open('a.txt',mode='r',encoding='utf-8') f=MyOpen('aaa.py',mode='r',encoding='utf-8') print(f.filepath,f.mode,f.encoding) print(f) print(f.fobj) res=f.fobj.read() print(res)
五、元类
定义：
元类：类的类就是元类
code="""
# global x
# x=0
# y=2
# """
# global_dic={'x':100000}
# local_dic={}
# exec(code,global_dic,local_dic)
#
# print(global_dic)
# print(local_dic)
#
# code="""
# x=1
# y=2
# def f1(self,a,b):
# pass
# """
# local_dic={}
# exec(code,{},local_dic)
# print(local_dic)
#
#1、一切皆为对象：
# Chinese=type(...)
# class Chinese:
# country="China"
#
# def __init__(self,name,age,sex):
# self.name=name
# self.age=age
# self.sex=sex
#
# def speak(self):
# print('%s speak Chinese' %self.name)
#
# print(Chinese)
# p=Chinese('egon',18,'male')
# print(type(p))
# print(type(Chinese))
# 元类：类的类就是元类，
#我们用class定义的类使用来产生我们自己的对象的
#内置元类type是用来专门产生class定义的类的
class Foo: #Foo=type(...)
pass
# print(type(Foo))
# f=Foo
#
# l=[Foo,]
# print(l)
#2、用内置的元类type，来实例化得到我们的类
# class_name='Chinese'
# class_bases=(object,)
# class_body="""
# country="China"
# def __init__(self,name,age,sex):
# self.name=name
# self.age=age
# self.sex=sex
# def speak(self):
# print('%s speak Chinese' %self.name)
# """
# class_dic={}
# exec(class_body,{},class_dic)
# 类的三大要素
# print(class_name,class_bases,class_dic)
# Chinese=type(class_name,class_bases,class_dic)
# print(Chinese)
# p=Chinese('egon',18,'male')
# print(p.name,p.age,p.sex)
#3、储备知识__call__
# class Foo:
# def __init__(self):
# pass
# def __str__(self):
# return '123123'
#
# def __del__(self):
# pass
#
# # 调用对象，则会自动触发对象下的绑定方法__call__的执行，
# # 然后将对象本身当作第一个参数传给self，将调用对象时括号内的值
# #传给*args与**kwargs
# def __call__(self, *args, **kwargs):
# print('__call__',args,kwargs)
#
#
# obj=Foo()
# # print(obj)
#
# obj(1,2,3,a=1,b=2,c=3) #
# #4 、自定义元类：
# class Mymeta(type):
# # 来控制类Foo的创建
# def __init__(self,class_name,class_bases,class_dic): #self=Foo
# # print(class_name)
# # print(class_bases)
# # print(class_dic)
# if not class_name.istitle():
# raise TypeError('类名的首字母必须大写傻叉')
#
# if not class_dic.get('__doc__'):
# raise TypeError('类中必须写好文档注释，大傻叉')
#
# super(Mymeta,self).__init__(class_name,class_bases,class_dic)
#
# # 控制类Foo的调用过程，即控制实例化Foo的过程
# def __call__(self, *args, **kwargs): #self=Foo,args=(1111,) kwargs={}
# # print(self)
# # print(args)
# # print(kwargs)
#
# #1 造一个空对象obj
# obj=object.__new__(self)
#
# #2、调用Foo.__init__,将obj连同调用Foo括号内的参数一同传给__init__
# self.__init__(obj,*args,**kwargs)
#
# return obj
#
#
#
# #Foo=Mymeta('Foo',(object,),class_dic)
# class Foo(object,metaclass=Mymeta):
# """
# 文档注释
# """
# x=1
# def __init__(self,y):
# self.Y=y
#
# def f1(self):
# print('from f1')
#
#
# obj=Foo(1111) #Foo.__call__()
#
# # print(obj)
# # print(obj.y)
# # print(obj.f1)
# # print(obj.x)
# 单例模式
import settings
class MySQL:
__instance=None
def __init__(self,ip,port):
self.ip=ip
self.port=port
@classmethod
def singleton(cls):
if not cls.__instance:
obj=cls(settings.IP, settings.PORT)
cls.__instance=obj
return cls.__instance
obj1=MySQL('1.1.1.2',3306)
obj2=MySQL('1.1.1.3',3307)
obj3=MySQL('1.1.1.4',3308)
# obj4=MySQL(settings.IP,settings.PORT)
# print(obj4.ip,obj4.port)
obj4=MySQL.singleton()
obj5=MySQL.singleton()
obj6=MySQL.singleton()
print(obj4 is obj5 is obj6)