常量实例变量? [英] Constant instance variables?

问题描述

我使用@property来确保对对象实例变量的更改由我需要的方法包装.

I use @property to ensure that changes to an objects instance variables are wrapped by methods where I need to.

当实例具有逻辑上不应更改的变量时，该怎么办?例如，如果我要为Process创建类，则每个Process实例应具有一个PID属性，该属性将经常访问但不应更改.

What about when an instance has an variable that logically should not be changed? Eg, if I'm making a class for a Process, each Process instance should have a PID attribute that will frequently be accessed but should not be changed.

处理试图修改该实例变量的人的最Pythonic方式是什么?

What's the most Pythonic way to handle someone attempting to modify that instance variable?

• 仅信任用户不要尝试更改 他们不应该的东西吗?

• Simply trust the user not to try and change something they shouldn't?

使用属性，但引发一个 如果实例变量是 变了吗?

Use property but raise an exception if the instance variable is changed?

还有什么?

推荐答案

使用__前缀变量的名称，并创建只读属性，Python将处理异常，并且变量本身将受到保护，以防止意外覆盖

Prepend name of the variable with __, and create read-only property, Python will take care of exceptions, and variable itself will be protected from accidental overwrite.

class foo(object):
    def __init__(self, bar):
        self.__bar = bar

    @property
    def bar(self):
        return self.__bar

f = foo('bar')
f.bar         # => bar
f.bar = 'baz' # AttributeError; would have to use f._foo__bar

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