Python 类 元类 new之间的关系

import six
from abc import ABCMeta

class DictItem():
    pass


class ItemMeta(ABCMeta):
    def __new__(mcs, class_name, bases, attrs):
        print('mcs:%s . class_name:%s . base:%s . attrs:%s '%(mcs,class_name,bases,attrs))
        
        return super(ItemMeta, mcs).__new__(mcs, class_name, bases, attrs)

@six.add_metaclass(ItemMeta)
class Item(DictItem):
        pass


class Book(Item):
        name=2
        price=3

book2=Book()

输出为：

mcs:<class '__main__.ItemMeta'> . class_name:Item . base:(<class '__main__.DictItem'>,) . attrs:{'__doc__': None, '__module__': '__main__'} //这个是Item类对象构造时的输出
mcs:<class '__main__.ItemMeta'> . class_name:Book . base:(<class '__main__.Item'>,) . attrs:{'__qualname__': 'Book', 'price': 3, '__module__': '__main__', 'name': 2} //这个是实例化book对象的输出