Python 自定义元类的两种写法

# 自定义元类
#继承type
class LowercaseMeta(type):
    ‘‘‘
    修改类的属性名称为小写的元类
    ‘‘‘
    # __new__ 类的实列的创建 #__init__类的初始化

    #方法一：
    def __new__(mcs,name,bases,attrs):
        lower_attrs={}
        for k,v in attrs.items():
            if not k.startswith(‘__‘): #排除magic method
                lower_attrs[k.lower()]=v
            else:
                lower_attrs[k]=v
        return type.__new__(mcs,name,bases,lower_attrs)

    # 方法二：
    # def __new__(cls, *args, **kwargs):
    #     #将要替换args
    #     new_args=[]
    #     for arg in args:
    #         if isinstance(arg,dict):
    #             low_attrs = {}
    #             for k,v in arg.items():
    #                 if str(k).startswith(‘__‘): #magic method
    #                     low_attrs[k]=v
    #                 else:       #排除magic method
    #                     low_attrs[str(k).lower()]=v
    #             new_args.append(low_attrs)
    #         else:
    #             new_args.append(arg)
    #     return type.__new__(cls,*new_args,**kwargs)

#类
class LowercaseClass(metaclass=LowercaseMeta): #py3
    BAR=True

    def HELLO(self):
        print(‘hello‘)

#此时BAT,HELLO   都变为小写
print(dir(LowercaseClass))
LowercaseClass().hello()