@property的妙用

1. 倒霉的程序员SA新建了这样一个简单的Student类：

   class Student:
   
       def __init__(self, score = 0):
           self.score = score

   然后各种使用这个Student类:

   s1 = Student()
   s1.score = 100
   s2 = Student()
   s2.score = 90
   s3 = Student()
   s3.score = 59
   s4 = Student()
   s4.score = -50
   
   print(s1.score)
   print(s2.score)
   print(s3.score)
   print(s4.score)

2. 后来SA在使用过程中发现，这样不行啊，怎么负数也可以，然后他把Student改造了一下:

   class Student:
   
       def __init__(self, score = 0):
           self._score = score
   
       def get_score(self):
           return self._score
   
       def set_score(self, value):
           if not isinstance(value, int):
               raise ValueError("score must be an interger!")
           if value < 0 or value > 100:
               raise ValueError("score must between 0~100!")
           self._score = value

   他得意洋洋地说，我这里用_score代替score是想告诉后来人：我不建议他直接调用_score属性。我们像下面这样用就可以规避别个乱入score啦：

   s1 = Student()
   s1.set_score(100)
   
   print(s1.get_score())

3. 后来SA发现，我去，要修改的地方太多啦！有没有更好的办法？还好他看到了廖雪峰的官方网站，原来还有@property这样神奇的用法：

   class Student:
       def __init__(self, score = 0):
           self._score = score
   
       @property
       def score(self):
           return self._score
   
       @score.setter
       def score(self, value):
           if not isinstance(value, int):
               raise ValueError("score must be an interger!")
           if value < 0 or value > 100:
               raise ValueError("score must between 0~100!")
           self._score = value

   这样，我原来写的那些代码不用修改就可以直接使用啦：

   s1 = Student()
   s1.score = 100
   s2 = Student()
   s2.score = 90
   s3 = Student()
   s3.score = 59
   s4 = Student()
   s4.score = -50
   
   print(s1.score)
   print(s2.score)
   print(s3.score)
   print(s4.score)

4. SA顿生感慨，有时间还是得多看看廖雪峰的官方网站啊！