Python学习10：@perporty

Posted 2023-02-03 CQ小子

本文学习Python的笔记，仅供参考

一般情况下在面向对象的编程中，属性不暴露在外面，而是通过一个接口函数去设置，比如下面的例子，定义了一个student的类，里面有两个私有的成员变量name和score，同时也有4个方法，print_name,set_name,set_socre,get_score。

class Student(object):
    def __init__(self,name,score):
        self.__name = name
        self.__score = score
    def print_name(self):
        print(self.__name)
    def set_name(self,name):
        self.__name = name
    def set_score(self,score):
        self.__score = score
    def get_score(self):
        return self.__score
bat = Student("zhangsan",99)
bat.print_name()
bat.set_name("lisi")
bat.print_name()
bat.set_score(88)
print(bat.get_score())

这四个成员函数分别用来获取和设置成员变量，从调用的状况来看，我设置name为lisi，成绩为88，执行结果为：

======================== RESTART: E:/python/class.py ========================
zhangsan
lisi
88

函数中没有进行参数检查，可以把参数检查的部分加上：

class Student(object):
    def __init__(self,name,score):
        self.__name = name
        self.__score = score
    def print_name(self):
        print(self.__name)
    def set_name(self,name):
        if not isinstance(name,str):
            raise ValueError("name must be an str")
        self.__name = name
    def set_score(self,score):
        if not isinstance(score,int):
            raise ValueError("score must be an int")
        if score < 0 or score > 100:
            raise ValueError("Score must between 0~100")
        self.__score = score
    def get_score(self):
        return self.__score

运行下设置score，产生了如期的错误

>>> bat.set_score(999)
Traceback (most recent call last):
  File "<pyshell#40>", line 1, in <module>
    bat.set_score(999)
  File "<pyshell#34>", line 15, in set_score
    raise ValueError("Score must between 0~100")
ValueError: Score must between 0~100

有没有既能检查参数，又可以用类似属性这样简单的方式来访问类的变量呢？对于追求完美的Python程序员来说，这是必须要做到的！ Python内置的 @property 装饰器就是负责把一个方法变成属性调用的：

@property可以把一个getter方法变成属性，同时又生成一个@score.setter把setter方法变成属性

class Student(object):
    def print_name(self):
        print(self.__name)
    def set_name(self,name):
        if not isinstance(name,str):
            raise ValueError("name must be an str")
        self.__name = name
    @property
    def score(self):
        return self.__score
    @score.setter
    def score(self,score):
        if not isinstance(score,int):
            raise ValueError("score must be an int")
        if score < 0 or score > 100:
            raise ValueError("Score must between 0~100")
        self.__score = score

实验下结果：

>>> bat.set_name("zhangsan")
>>> bat.score = 99
>>> bat.score
99
>>> bat.score = 1000
Traceback (most recent call last):
  File "<pyshell#47>", line 1, in <module>
    bat.score = 1000
  File "<pyshell#41>", line 16, in score
    raise ValueError("Score must between 0~100")
ValueError: Score must between 0~100

既能够参数检查，有能够像调用属性那样实际上去调用成员函数