python 类 描述符及应用

#描述符可以实现大部分python类特性中的底层魔法，包括，@classmethod @staticmethod @property甚至是__slots__
# class Typed:
#     def __init__(self,key,expected_type):
#         self.key=key
#         self.expected_type=expected_type
#     def __get__(self, instance, owner):
#         print('get_method...')
#         # print('instance参数[%s]' %instance)
#         # print('owner参数[%s]' %owner)
#         return instance.__dict__[self.key]
#     def __set__(self, instance, value):
#         print('set_method...')
#         # print('instance参数[%s]' %instance)
#         # print('value的参数[%s]' %value)
#         # print(instance.__dict__)
#         if not isinstance(value,self.expected_type):         #用于类型检查
#             # print('你传入类型错误...')
#             # return
#             raise TypeError('%s传入的类型不是%s...'%(self.key,self.expected_type))   #也可以用抛出异常方式
#         instance.__dict__[self.key]=value
#     def __delete__(self, instance):
#         print('delete_method...')
#         # print('instance参数[%s]' %instance)
#         instance.__dict__.pop(self.key)
#
# class People:
#     name=Typed('name',str)
#     age=Typed('age',int)
#     def __init__(self,name,age,salary):
#         self.name=name
#         self.age=age
#         self.salary=salary
# # p1=People('jack',19,39.4)
# # p1=People(3454,1522,39.4)    #传入错误的参数时
#
# print(p1.__dict__)
# # print(p1.name)
# #
# # p1.name='milk'
# # print(p1.__dict__)
# # del p1.name
# # print(p1.__dict__)