property装饰器的实现 & 描述器的深入思考

　　

　　

class Property:
    def __init__(self,fget=None,fset=None,fdel=None):
        self.fget=fget
        self.fset=fset
        self.fdel=fdel

    def __repr__(self):
        return 'self: {} fget: {} fset: {} fdel: {}'.format(id(self),self.fget,self.fset,self.fdel)

    def __get__(self,instance,owner):
        if instance is None:
            return self
        return self.fget(instance)

    def __set__(self,instance,value):
        if self.fset is None: # 未设置setter时,进行属性设置,抛出异常
            raise AttributeError('{} has no setter set'.format(instance.__class__.__name__))
        if instance is None: # class call
            return self
        self.fset(instance,value)

    def __delete__(self,instance):
        if self.fdel is None: # 未设置deleter时,删除属性,抛异常
            raise AttributeError('{} has no deleter set'.format(instance.__class__.__name__))
        if instance is None: # class call
            return self
        self.fdel(instance)

    def setter(self,fset):
        print(self.fget.__name__,fset.__name__)
        if self.fget.__name__ != fset.__name__: # setter 和 getter装饰的函数名字不同时,创建新描述器
            return Property(fset=fset)
        self.fset=fset
        return self
    def deleter(self,fdel):
        print(self.fset.__name__,fdel.__name__)
        if fdel.__name__ != self.fset.__name__: # deleter 和 setter装饰的函数名字不同时,创建新描述器
            return Property(fdel=fdel)
        self.fdel=fdel
        return self

class B:
    def __init__(self,data):
        self._data=data

    @Property # datum1=Property(datum)
    def datum1(self):
        return self._data
    @datum1.setter # datum2=datume1.setter(datum2)
    def datum2(self,value):
        self._data=value
    @datum2.deleter # datum3=datum2.deleter(datum3)
    def datum3(self):
        del self._data

print(B.datum1)
print(B.datum2)
print(B.datum3)
b=B(22)
print(b.datum1)
b.datum2=33
print(b.datum1)
print(b.__dict__)
del b.datum3
print(b.__dict__)