code="""
global x     
x=0
y=2
"""                           #字符串内声明的名称是全局，其他为局部名称
global_dic={'x':100000}
local_dic={}                   # 运行字符串内代码
exec(code,global_dic,local_dic) # 把全局名称空间的名称放入global_dic，把局部的放入local_dic
​
print(global_dic)              #{'x': 0}
print(local_dic)               #{'y': 2}

class_name='Chinese'
class_bases=(object,)   #基类
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 (<class 'object'>,) {'country':'China', '__init__': <function __init__ at ...>, 'speak': <function speak at....>}
​
Chinese=type(class_name,class_bases,class_dic)  #实例化一个类
print(Chinese)                               #<class '__main__.Chinese'>
​
p=Chinese('egon',18,'male')  #实例化对象p
print(p.name,p.age,p.sex)    # egon 18 male  #说明和class定义的类功能相同

class Foo:
     def __init__(self):
         pass
​
     def __call__(self, *args, **kwargs):# 调用对象，则会自动触发对象下的绑定方法__call__的执行，
         print('__call__',*args, **kwargs)# 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
obj=Foo()
obj(1,2,3,a=1,b=2,c=3) #对象调用

class Mymeta(type):   
     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():                       #控制类名首字母必须大写
             raise TypeError('类名的首字母必须大写傻叉')
​
         if not class_dic.get('__doc__'):                   # 控制文档注释必须存在
             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)  #重用父类功能
#Foo=Mymeta('Foo',(object,),class_dic)
class Foo(object,metaclass=Mymeta): # metaclass=Mymeta创建自定义元类
     """
     文档注释
     """

class Mymeta(type):   
     def __init__(self,class_name,class_bases,class_dic): #self=Foo
         print(class_name)
         print(class_bases)
         print(class_dic)
        
     def __call__(self, *args, **kwargs): #self=Foo,args=(1111,) 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): 
     x=1
     def __init__(self,y):
         self.y=y
​
     def f1(self):
         print('from f1')
obj=Foo(1111)           #Foo.__call__()
print(obj)              #<__main__.Foo object at 0x000002019EE1BB70>
print(obj.y)            # 1111
print(obj.f1)           #<bound method Foo.f1 of <__main__.Foo object at 0x000002019EE1BB70>>
print(obj.x)            # 1

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.singleton()          # obj4=MySQL(settings.IP,settings.PORT)
obj5=MySQL.singleton()
obj6=MySQL.singleton()
print(obj4.ip,obj4.port)        # 1.1.1.1 3306
​
print(obj4 is obj5 is obj6)     # True