Python-属性描叙符协议ORM实现原理依据- __set__ __get__ __delete__

Posted 2020-11-11 北门吹雪

class CheckString:
    def __init__(self, variable_type):
        self.variable_type = variable_type

    def __set__(self, instance, value):
        print(‘__set__:‘, value)
        self.value = "error：类型错误"
        if self.variable_type == ‘str‘:
            self.value = value if isinstance(value, str) else "error：类型错误"

    def __get__(self, instance, owner):
        print("__get__")
        return self.value
        pass

    def __delete__(self, instance):
        pass


class InfoModel:
    name = CheckString(variable_type=‘str‘)


if __name__ == ‘__main__‘:
    info = InfoModel()
    info.name = "北门吹雪"
    print(info.name)

通过另外一个类来描叙类变量的属性类型，这个是ORM实现的核心基础

给属性赋值会调用 __set__方法，访问属性则会调用 __get__方法，则可以获取字段的对象和其值，删除字段时候则调用 __delete__方法