python中@property的使用

在绑定属性时,如果我们将属性直接暴露在外面,就可能导致属性被任意修改,有时候这个是我们不希望看到的
如:设置学生的成绩
class Student(object):
    def __init__(self):
        self.score = 0
#这个显然不符合属性的规范
#std = Student()
#std.score = 99999
#print std.score
#于是我们采用内部限制的方法来设定
 1 class Student2(object):
 2     def __init__(self):
 3         pass
 4 
 5     def get_score(self):
 6         return self._score
 7 
 8     def set_score(self, value):
 9         if not isinstance(value, int):
10             raise ValueError('score must be an integer!')
11         if value < 0 or value > 100:
12             raise ValueError('score must between 0 ~ 100!')
13         self._score = value
14 
15 
16 std2 = Student2()
17 std2.set_score(60)
18 print std2.get_score() #60
19 
20 std2.set_score(99999)
21 print std2.get_score()
22 
23 Traceback (most recent call last):
24   File "/home/mywork/oldboy/practice/property.py", line 44, in <module>
25     std2.set_score(99999)
26   File "/home/mywork/oldboy/practice/property.py", line 35, in set_score
27     raise ValueError('score must between 0 ~ 100!')
28 ValueError: score must between 0 ~ 100!
#但是,上面的调用方法又略显复杂,这就是需要应用@property
#他的本质就是把一个getter方法变成属性
#此时,@property本身又创建了另一个装饰器@score.setter,
#负责把一个setter方法变成属性赋值,于是,我们就拥有一个可控的属性操作:
看代码:
 1 class Student3(object):
 2 
 3     @property
 4     def score(self):
 5         return self._score
 6 
 7     @score.setter
 8     def score(self, value):
 9         if not isinstance(value, int):
10             raise ValueError('score must be an integer!')
11         if value < 0 or value > 100:
12             raise ValueError('score must between 0 ~ 100!')
13         self._score = value
14 
15 std3 = Student3()
16 std3.score = 90
17 print std3.score #90
18 std3.score = 9000 #直接设置时就报错
19 
20 Traceback (most recent call last):
21   File "/home/mywork/oldboy/practice/property.py", line 69, in <module>
22     std3.score = 9000
23   File "/home/mywork/oldboy/practice/property.py", line 63, in score
24     raise ValueError('score must between 0 ~ 100!')
25 ValueError: score must between 0 ~ 100!

 

posted @ 2017-03-13 12:04  北京流浪儿  阅读(333)  评论(0编辑  收藏  举报