property在python2和py

发布时间:2019-10-18 09:07:11编辑:auto阅读(565)

    • 问题背景: 源于公司的原来的代码是python2开发的,后来改为python3开发,设计到的property的用法有点不一样
    • 直接上代码

    公司原来的python2的代码

    class LineItem:
    
        def __init__(self, description, weight, price):
            self.description = description
            self.__weight = weight
            self.price = price
    
        @property
        def weight(self):
            return self.__weight
    
        @weight.setter
        def set_weight(self, value):
            if value > 0:
                self.__weight = value
            else:
                raise ValueError('weight must be > 0')

    运行代码

    In [2]: l = LineItem('a', 3, 6)
    
    In [3]: l.weight
    Out[3]: 3
    
    In [4]: l.weight = 5
    
    In [5]: l.weight
    Out[5]: 5

    这个代码在python2下面执行没有问题,但是在python3下面执行,会报错,在执行In [4]: l.weight = 5的时候报错

    In [4]: l.weight = 5
    ---------------------------------------------------------------------------
    AttributeError                            Traceback (most recent call last)
    <ipython-input-4-3c1df6104a5e> in <module>
    ----> 1 l.weight = 5
    
    AttributeError: can't set attribute
    • 解决方法

    按理说,上面的那种写法不是很规范,无论是在python2还是python3的文档实例里面都不是这么写的,所以为了简便和不出错,我们统一使用下面的这种写法

    class LineItem:
    
        def __init__(self, description, weight, price):
            self.description = description
            self.__weight = weight
            self.price = price
    
        @property
        def weight(self):
            return self.__weight
    
        @weight.setter
        def weight(self, value):
            if value > 0:
                self.__weight = value
            else:
                raise ValueError('weight must be > 0')

    主要区别在于这一行def weight(self, value):

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