# -*- coding: utf-8 -*-"""Created on Tue Mar 19 22:48:17 2019@author: fengs""""""测试题:0. 请尽量用自己的语言来解释什么是描述符（不要搜索来的答案，用自己的话解释）？ 绑定属性的 set & get & del 方法""""""1. 描述符类中，分别通过哪些魔法方法来实现对属性的 get、set 和 delete 操作的？ __get__ __set__ __delete__""""""2. 请问以下代码，分别调用 test.a 和 test.x，哪个会打印“getting…”?class MyDes: def __get__(self, instance, owner): print("getting...")class Test: a = MyDes() x = atest = Test()test.atest.x#都会打印 getting """"""class MyDes: def __get__(self, instance, owner): print("getting...") return 1class Test: a = MyDes() x = atest = Test()print(test.a)print(test.x)""""""3. 请问以下代码会打印什么内容？class MyDes: def __init__(self, value = None): self.val = value def __get__(self, instance, owner): return self.val - 20 def __set__(self, instance, value): self.val = value + 10 print(self.val)class C: x = MyDes()if __name__ == '__main__': # 该模块被执行的话，执行下边语句。 c = C() c.x = 10 print(c.x) 20 __set__中打印 0 __get__中打印""""""4. 请问以下代码会打印什么内容？class MyDes: def __init__(self, value = None): self.val = value def __get__(self, instance, owner): return self.val ** 2class Test: x = MyDes(3) def __init__(self): #self.x = MyDes(3)test = Test()test.xx 并非类属性，test.x的结果将是一个描述符对象"""class MyDes: def __init__(self, value = None): self.val = value def __get__(self, instance, owner): return self.val ** 2class Test: x = MyDes(3) def __init__(self): pass #self.x = MyDes(3)#test = Test()#print(test.x)"""动动手（一定要自己动手试试哦~）：0. 按要求编写描述符 MyDes：当类的属性被访问、修改或设置的时候，分别做出提醒。程序实现如下：>>> class Test: x = MyDes(10, 'x')>>> test = Test()>>> y = test.x正在获取变量： x>>> y10>>> test.x = 8正在修改变量： x>>> del test.x正在删除变量： x噢~这个变量没法删除~>>> test.x正在获取变量： x8""" class MyDes0(): def __init__(self,value = None,name = None): self.value = value self.name = name def __get__(self,instance,owner): print('正在获取变量: %s ' % self.name ) return self.value def __set__(self,instance,value): print('正在修改变量: %s' % self.name ) self.value = value def __delete__(self,instance): print('正在删除变量: %s' % self.name ) print('噢=.=,这个变量没法删除') return Noneclass Test0(): x = MyDes0(10,'x')#test0 = Test0()#print(test0.x)#test0.x = 8#del test0.x#print(test0.x)"""1. 按要求编写描述符 MyDes：记录指定变量的读取和写入操作，并将记录以及触发时间保存到文件（record.txt）程序实现如下：>>> class Test: x = Record(10, 'x') y = Record(8.8, 'y')>>> test = Test()>>> test.x10>>> test.y8.8>>> test.x = 123>>> test.x = 1.23>>> test.y = "I love FishC.com!">>>"""import timeclass Record(): def __init__(self,value,name): self.value = value self.name = name self.fileSaveName = "record.txt" def append_line_to_txt(self,txt_line): with open(self.fileSaveName,'a') as fid: fid.write(txt_line) def __get__(self,instance,owner): now = time.asctime() txt_line = "%s 变量于北京时间 %s 被读取, %s = %s \n" % (self.name,now,self.name,self.value) self.append_line_to_txt(txt_line) return self.value def __set__(self,instance,value): now = time.asctime() self.value = value txt_line = "%s 变量于北京时间 %s 被修改, %s = %s \n" % (self.name,now,self.name,self.value) self.append_line_to_txt(txt_line) class Test1(): x = Record(10,'x') y = Record(8.8,'y')test1 = Test1()print(test1.x)print(test1.y)test1.x = 123test1.x = 1.23test1.y = "I love FishC.com!""""2. 再来一个有趣的案例：编写描述符 MyDes，使用文件来存储属性，属性的值会直接存储到对应的pickle（腌菜，还记得吗？）的文件中。如果属性被删除了，文件也会同时被删除，属性的名字也会被注销。举个栗子：>>> class Test: x = MyDes('x') y = MyDes('y') >>> test = Test()>>> test.x = 123>>> test.y = "I love FishC.com!">>> test.x123>>> test.y'I love FishC.com!'产生对应的文件存储变量的值："""import os import pickleclass MyDes2(): def __init__(self,name): self.name = name self.value = None self.file_name = self.name + '.pkl' def __get__(self,instance,owner): with open(self.file_name,'rb') as fid: self.value = pickle.load(fid) return self.value def __set__(self,instance,value): self.value = value with open(self.file_name,'wb') as fid: pickle.dump(self.value,fid) def __delete__(self,instance): os.remove(self.file_name) class Test2(): x = MyDes2('x') y = MyDes2('y') test2 = Test2()test2.x = 123test2.y = 'I love Fishc.Com!'print(test2.x)print(test2.y)#del test2.x