如何在Python类中为非函数成员属性创建别名？ [英] How can I make an alias to a non-function member attribute in a Python class?

问题描述

我正在编写一个Python库API，我经常遇到用户需要为同一个函数和变量使用多个不同名称的情况。

I'm in the midst of writing a Python Library API and I often run into the scenario where my users want multiple different names for the same functions and variables.

如果我有一个Python类的函数 foo（），我想要一个别名为 bar（），这很容易：

If I have a Python class with the function foo() and I want to make an alias to it called bar(), that's super easy:

class Dummy(object):

   def __init__(self):
      pass

   def foo(self):
      pass

   bar = foo

现在我可以这样做没有问题：

Now I can do this with no problem:

d = Dummy()
d.foo()
d.bar()

我想知道什么是最好的方法来做这个类属性是一个常规变量（例如字符串），而不是一个函数？如果我有这段代码：

What I'm wondering is what is the best way to do this with a class attribute that is a regular variable (e.g. a string) rather than a function? If I had this piece of code:

d = Dummy()
print d.x
print d.xValue

我想要 dx 和 d.xValue 到始终打印同样的内容。如果 dx 更改，它也应该更改 d.xValue （反之亦然）。

I want d.x and d.xValue to ALWAYS print the same thing. If d.x changes, it should change d.xValue also (and vice-versa).

我可以想到很多方法来做到这一点，但没有一个看起来像我想要的那么光滑：

I can think of a number of ways to do this, but none of them seem as smooth as I'd like:

• 编写自定义注释


• 使用 @property 注释并与设置器混淆


• 覆盖 __ setattr __ 类函数

• Write a custom annotation
• Use the @property annotation and mess with the setter
• Override the __setattr__ class functions

是最好的？还是有另一种方式？我不禁感到，如果它很容易使函数的别名，它应该是任意变量一样容易...

Which of these ways is best? Or is there another way? I can't help but feel that if it's so easy to make aliases for functions, it should be just as easy for arbitrary variables...

FYI：我使用Python 2.7.x，而不是Python 3.0，所以我需要一个Python 2.7.x兼容的解决方案（虽然我会感兴趣，如果Python 3.0做一些直接解决这个需要）。

FYI: I'm using Python 2.7.x, not Python 3.0, so I need a Python 2.7.x compatible solution (though I would be interested if Python 3.0 does something to directly address this need).

谢谢！

推荐答案

您可以提供 __ setattr __ code> __ getattr __ 引用别名映射：

You can provide a __setattr__ and __getattr__ that reference an aliases map:

class Dummy(object):
    aliases = {
        'xValue': 'x',
        'another': 'x',
        }

    def __init__(self):
        self.x = 17

    def __setattr__(self, name, value):
        name = self.aliases.get(name, name)
        object.__setattr__(self, name, value)

    def __getattr__(self, name):
        if name == "aliases":
            raise AttributeError  # http://nedbatchelder.com/blog/201010/surprising_getattr_recursion.html
        name = self.aliases.get(name, name)
        #return getattr(self, name) #Causes infinite recursion on non-existent attribute
        return object.__getattribute__(self, name)


d = Dummy()
assert d.x == 17
assert d.xValue == 17
d.x = 23
assert d.xValue == 23
d.xValue = 1492
assert d.x == 1492

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