元类编程-- metaclass

Posted 2020-10-31 Erick - LONG

#类也是对象，type创建类的类
def create_class(name):
    if name == "user":
        class User:
            def __str__(self):
                return "user"
        return User
    elif name == "company":
        class Company:
            def __str__(self):
                return "company"
        return Company

#type动态创建类
# User = type("User", (), {}) #名称，继承（要继承的base类），属性或方法（但是要字典形式）

def say(self):
    return "i am user"
    # return self.name


class BaseClass():
    def answer(self):
        return "i am baseclass"


class MetaClass(type): #继承type为元类
    def __new__(cls, *args, **kwargs):
        return super().__new__(cls, *args, **kwargs)

from collections.abc import *

#什么是元类， 元类是创建类的类 对象<-class(对象)<-type
class User(metaclass=MetaClass):
    def __init__(self, name):
        self.name = name
    def __str__(self):
        return "user"
#python中类的实例化过程，会首先寻找metaclass，通过metaclass去创建user类
#type去创建类对象，实例

if __name__ == "__main__":
    # MyClass = create_class("user")
    # my_obj = MyClass()
    # print(type(my_obj))

    # User = type("User", (BaseClass, ), {"name":"user", "say":say})
    my_obj = User(name="bobby")
    print(my_obj)