元类
元类
一切源自于一句话：python中一切皆为对象
一：元类介绍
"""
元类=》OldboyTeacher类=》obj
代码
class OldboyTeacher(object):
school = 'oldboy'
def __init__(self, name, age):
self.name = name
self.age = age
def say(self):
print('%s says welcome to the oldboy to learn Python' % self.name)
obj = OldboyTeacher('egon', 18) # 调用OldboyTeacher类=》对象obj
调用元类=》OldboyTeacher类
print(type(obj))
print(type(OldboyTeacher))
结论：默认的元类是type，默认情况下我们用class关键字定义的类都是由type产生的
"""
二：class关键字底层的做了哪些事
'''
class_name = "OldboyTeacher"
2、然后拿到类的父类
class_bases = (object,)
3、再运行类体代码，将产生的名字放到名称空间中
class_dic = {}
class_body = """
school = 'oldboy'
def __init__(self, name, age):
self.name = name
self.age = age
def say(self):
print('%s says welcome to the oldboy to learn Python' % self.name)
"""
exec(class_body,{},class_dic)
print(class_dic)
4、调用元类（传入类的三大要素：类名、基类、类的名称空间）得到一个元类的对象，然后将元类的对象赋值给变量名OldboyTeacher,oldboyTeacher就是我们用class自定义的那个类
OldboyTeacher = type(class_name,class_bases,class_dic)
'''
三：自定义元类
'''
class Mymeta(type): # 只有继承了type类的类才是自定义的元类
pass
class OldboyTeacher(object, metaclass=Mymeta):
school = 'oldboy'
def __init__(self, name, age):
self.name = name
self.age = age
def say(self):
print('%s says welcome to the oldboy to learn Python' % self.name)
1、先拿到一个类名:"OldboyTeacher"
2、然后拿到类的父类:(object,)
3、再运行类体代码，将产生的名字放到名称空间中{...}
4、调用元类（传入类的三大要素：类名、基类、类的名称空间）得到一个元类的对象，然后将元类的对象赋值给变量名OldboyTeacher,oldboyTeacher就是我们用class自定义的那个类
OldboyTeacher = Mymeta("OldboyTeacher",(object,),{...})
'''
四：自定义元类来控制OldboyTeacher类的产生
'''
import re
class Mymeta(type): # 只有继承了type类的类才是自定义的元类
def init(self, class_name, class_bases, class_dic):
# print(self) # 类<class 'main.OldboyTeacher'>
# print(class_name)
# print(class_bases)
# print(class_dic)
if not re.match("[A-Z]", class_name):
raise BaseException("类名必须用驼峰体")
if len(class_bases) == 0:
raise BaseException("至少继承一个父类")
# print("文档注释：",class_dic.get('__doc__'))
doc=class_dic.get('__doc__')
if not (doc and len(doc.strip()) > 0):
raise BaseException("必须要有文件注释，并且注释内容不为空")
OldboyTeacher = Mymeta("OldboyTeacher",(object,),{...})
class OldboyTeacher(object,metaclass=Mymeta):
"""
adsaf
"""
school = 'oldboy'
def __init__(self, name, age):
self.name = name
self.age = age
def say(self):
print('%s says welcome to the oldboy to learn Python' % self.name)
'''
五：自定义元类来控制OldboyTeacher类的调用
'''
import re
class Mymeta(type): # 只有继承了type类的类才是自定义的元类
def init(self, class_name, class_bases, class_dic):
# print(self) # 类<class 'main.OldboyTeacher'>
# print(class_name)
# print(class_bases)
# print(class_dic)
if not re.match("[A-Z]", class_name):
raise BaseException("类名必须用驼峰体")
if len(class_bases) == 0:
raise BaseException("至少继承一个父类")
# print("文档注释：",class_dic.get('__doc__'))
doc = class_dic.get('__doc__')
if not (doc and len(doc.strip()) > 0):
raise BaseException("必须要有文件注释，并且注释内容不为空")
# res = OldboyTeacher('egon',18)
def __call__(self, *args, **kwargs):
# 1、先创建一个老师的空对象
tea_obj = object.__new__(self)
# 2、调用老师类内的__init__函数，然后将老师的空对象连同括号内的参数的参数一同传给__init__
self.__init__(tea_obj, *args, **kwargs)
tea_obj.__dict__ = {"_%s__%s" %(self.__name__,k): v for k, v in tea_obj.__dict__.items()}
# 3、将初始化好的老师对象赋值给变量名res
return tea_obj
OldboyTeacher = Mymeta("OldboyTeacher",(object,),{...})
class OldboyTeacher(object, metaclass=Mymeta):
"""
adsaf
"""
school = 'oldboy'
# tea_obj,'egon',18
def __init__(self, name, age):
self.name = name # tea_obj.name='egon'
self.age = age # tea_obj.age=18
def say(self):
print('%s says welcome to the oldboy to learn Python' % self.name)
res = OldboyTeacher('egon', 18)
print(res.dict)
print(res.name)
print(res.age)
print(res.say)
调用OldboyTeacher类做的事情：
1、先创建一个老师的空对象
2、调用老师类内的init方法，然后将老师的空对象连同括号内的参数的参数一同传给init
3、将初始化好的老师对象赋值给变量名res
'''
六：单例模式
单例模式就是确保一个类只有一个实例.当你希望整个系统中,某个类只有一个实例时,单例模式就派上了用场.
比如,某个服务器的配置信息存在在一个文件中,客户端通过AppConfig类来读取配置文件的信息.如果程序的运行的过程中,很多地方都会用到配置文件信息,则就需要创建很多的AppConfig实例,这样就导致内存中有很多AppConfig对象的实例,造成资源的浪费.其实这个时候AppConfig我们希望它只有一份,就可以使用单例模式.
实现方式1：classmethod
"""
import settings
class MySQL:
__instance = None
def __init__(self, ip, port):
self.ip = ip
self.port = port
@classmethod
def singleton(cls):
if cls.__instance:
return cls.__instance
cls.__instance = cls(settings.IP, settings.PORT)
return cls.__instance
obj1=MySQL("1.1.1.1",3306)
obj2=MySQL("1.1.1.2",3306)
print(obj1)
print(obj2)
obj3 = MySQL.singleton()
print(obj3)
obj4 = MySQL.singleton()
print(obj4)
"""
方式2：元类
"""
import settings
class Mymeta(type):
instance = None
def init(self,class_name,class_bases,class_dic):
self.instance=object.new(self) # Mysql类的对象
self.init(self.__instance,settings.IP,settings.PORT)
def __call__(self, *args, **kwargs):
if args or kwargs:
obj = object.__new__(self)
self.__init__(obj, *args, **kwargs)
return obj
else:
return self.__instance
MySQL=Mymeta(...)
class MySQL(metaclass=Mymeta):
def init(self, ip, port):
self.ip = ip
self.port = port
obj1 = MySQL("1.1.1.1", 3306)
obj2 = MySQL("1.1.1.2", 3306)
print(obj1)
print(obj2)
obj3 = MySQL()
obj4 = MySQL()
print(obj3 is obj4)
"""
方式3：装饰器
"""
import settings
def outter(func): # func = MySQl类的内存地址
_instance = func(settings.IP,settings.PORT)
def wrapper(args,**kwargs):
if args or kwargs:
res=func(args,**kwargs)
return res
else:
return _instance
return wrapper
@outter # MySQL=outter(MySQl类的内存地址) # MySQL=》wrapper
class MySQL:
def init(self, ip, port):
self.ip = ip
self.port = port
obj1 = MySQL("1.1.1.1", 3306)
obj2 = MySQL("1.1.1.2", 3306)
print(obj1)
print(obj2)
obj3 = MySQL()
obj4 = MySQL()
print(obj3 is obj4)
"""
了解：属性查找
class Mymeta(type):
n=444
# def __call__(self, *args, **kwargs): #self=<class '__main__.OldboyTeacher'>
# obj=self.__new__(self)
# print(self.__new__ is object.__new__) #True
class Bar(object):
# n=333
# def __new__(cls, *args, **kwargs):
# print('Bar.__new__')
pass
class Foo(Bar):
# n=222
# def __new__(cls, *args, **kwargs):
# print('Foo.__new__')
pass
class OldboyTeacher(Foo,metaclass=Mymeta):
# n=111
school='oldboy'
def __init__(self,name,age):
# self.n=0
self.name=name
self.age=age
def say(self):
print('%s says welcome to the oldboy to learn Python' %self.name)
# def __new__(cls, *args, **kwargs):
# print('OldboyTeacher.__new__')
obj=OldboyTeacher('egon',18)
print(obj.n)
print(OldboyTeacher.n)
call控制类的调用
class Foo:
def __call__(self, *args, **kwargs):
print('================>')
print(self)
print(args)
print(kwargs)
obj1 = Foo()
obj1(1,2,3,a=1,b=2) # 调用对象其实就是在调用对象类中定义的绑定方法__call__
#
# obj2 = int(10)
# obj2()
# obj3 = list([1, 2, 3])
# obj3()
