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

 class Student2(object):
     def __init__(self):
         pass

     def get_score(self):
         return self._score

     def set_score(self, value):
         if not isinstance(value, int):
             raise ValueError('score must be an integer!')
         if value < 0 or value > 100:
             raise ValueError('score must between 0 ~ 100!')
         self._score = value

 std2 = Student2()
 std2.set_score(60)
 print std2.get_score() #

 std2.set_score(99999)
 print std2.get_score()

 Traceback (most recent call last):
   File "/home/mywork/oldboy/practice/property.py", line 44, in <module>
     std2.set_score(99999)
   File "/home/mywork/oldboy/practice/property.py", line 35, in set_score
     raise ValueError('score must between 0 ~ 100!')
 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：

 class Student3(object):

     @property
     def score(self):
         return self._score

     @score.setter
     def score(self, value):
         if not isinstance(value, int):
             raise ValueError('score must be an integer!')
         if value < 0 or value > 100:
             raise ValueError('score must between 0 ~ 100!')
         self._score = value

 std3 = Student3()
 std3.score = 90
 print std3.score #
 std3.score = 9000 #直接设置时就报错

 Traceback (most recent call last):
   File "/home/mywork/oldboy/practice/property.py", line 69, in <module>
     std3.score = 9000
   File "/home/mywork/oldboy/practice/property.py", line 63, in score
     raise ValueError('score must between 0 ~ 100!')
 ValueError: score must between 0 ~ 100!