验证类实例的属性的正确方法 [英] Correct approach to validate attributes of an instance of class

问题描述

拥有一个简单的Python类：

Having a simple Python class like this:

class Spam(object):
    __init__(self, description, value):
        self.description = description
        self.value = value

我想检查以下限制：

• 描述不能为空


• 值必须大于零

我应该：

1.创建垃圾邮件对象之前验证数据？ br>
2.检查 __ init __ 方法上的数据？

3.创建一个 is_valid 方法在垃圾邮件类，并用spam.isValid（）？调用？

4.在垃圾邮件类上创建一个 is_valid 静态方法，并将其调用Spam.isValid（描述，价值）？

5.检查设定者声明的数据？

6.等

Should I:
1. validate data before creating spam object ?
2. check data on __init__ method ?
3. create an is_valid method on Spam class and call it with spam.isValid() ?
4. create an is_valid static method on Spam class and call it with Spam.isValid(description, value) ?
5. check data on setters declaration ?
6. etc.

你可以推荐一个精心设计的/ Pythonic /不是冗长的（在类上有许多属性）/优雅的方法？

Could you recommend a well designed/Pythonic/not verbose (on class with many attributes)/elegant approach?

推荐答案

您可以使用Python 属性清理适用规则分配到每个字段，并执行它们，即使客户端代码尝试更改字段：

You can use Python properties to cleanly apply rules to each field separately, and enforce them even when client code tries to change the field:

class Spam(object):
    def __init__(self, description, value):
        self.description = description
        self.value = value

    @property
    def description(self):
        return self._description

    @description.setter
    def description(self, d):
        if not d: raise Exception("description cannot be empty")
        self._description = d

    @property
    def value(self):
        return self._value

    @value.setter
    def value(self, v):
        if not (v > 0): raise Exception("value must be greater than zero")
        self._value = v

即使在 __ init __ 函数中，任何违反规则的尝试都将抛出异常，在这种情况下，对象构造将失败。

An exception will be thrown on any attempt to violate the rules, even in the __init__ function, in which case object construction will fail.

更新：在2010年和现在之间的某个时间，我了解了 operator.attrgetter ：

UPDATE: Sometime between 2010 and now, I learned about operator.attrgetter:

import operator

class Spam(object):
    def __init__(self, description, value):
        self.description = description
        self.value = value

    description = property(operator.attrgetter('_description'))

    @description.setter
    def description(self, d):
        if not d: raise Exception("description cannot be empty")
        self._description = d

    value = property(operator.attrgetter('_value'))

    @value.setter
    def value(self, v):
        if not (v > 0): raise Exception("value must be greater than zero")
        self._value = v

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