from datetime import date, datetime
import numbers
class IntField:
#数据描述符
def __get__(self, instance, owner):
return self.value
def __set__(self, instance, value):
if not isinstance(value, numbers.Integral):
raise ValueError("int value need")
if value < 0:
raise ValueError("positive value need")
self.value = value
def __delete__(self, instance):
pass
class NonDataIntField:
#非数据属性描述符
def __get__(self, instance, owner):
return self.value
class User:
age = IntField()
# age = NonDataIntField()
'''
如果user是某个类的实例,那么user.age(以及等价的getattr(user,’age’))
首先调用__getattribute__。如果类定义了__getattr__方法,
那么在__getattribute__抛出 AttributeError 的时候就会调用到__getattr__,
而对于描述符(__get__)的调用,则是发生在__getattribute__内部的。
user = User(), 那么user.age 顺序如下:
(1)如果“age”是出现在User或其基类的__dict__中, 且age是data descriptor, 那么调用其__get__方法, 否则
(2)如果“age”出现在user的__dict__中, 那么直接返回 obj.__dict__[‘age’], 否则
(3)如果“age”出现在User或其基类的__dict__中
(3.1)如果age是non-data descriptor,那么调用其__get__方法, 否则
(3.2)返回 __dict__[‘age’]
(4)如果User有__getattr__方法,调用__getattr__方法,否则
(5)抛出AttributeError
'''
# class User:
#
# def __init__(self, name, email, birthday):
# self.name = name
# self.email = email
# self.birthday = birthday
# self._age = 0
#
# # def get_age(self):
# # return datetime.now().year - self.birthday.year
#
# @property
# def age(self):
# return datetime.now().year - self.birthday.year
#
# @age.setter
# def age(self, value):
# #检查是否是字符串类型
# self._age = value
if __name__ == "__main__":
user = User()
user.__dict__["age"] = "abc"
print (user.__dict__)
print (user.age)
# print (getattr(user, 'age'))
# user = User("bobby", date(year=1987, month=1, day=1))
# user.age = 30
# print (user._age)
# print(user.age)
【python】属性描述符访问属性的顺序
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转载自blog.csdn.net/qq_38065133/article/details/82598229
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