Create an alias to an attribute on superclass

[Ian Kelly]

On Thu, Feb 1, 2018 at 11:44 AM, Sean DiZazzo <sean.dizazzo at gmail.com> wrote:
> On Thursday, February 1, 2018 at 10:37:32 AM UTC-8, Chris Angelico wrote:
>> On Fri, Feb 2, 2018 at 5:22 AM, Sean DiZazzo <sean.dizazzo at gmail.com> wrote:
>> > Hi!
>> >
>> > I basically just want to create an alias to an attribute on an item's superclass.  So that after I create the subclass object, I can access the alias attribute to get the value back.
>> >
>> > <pre>
>> > class Superclass(object):
>> >     def __init__(self, value):
>> >         """
>> >             I want to pass x by reference, so that any time
>> >             x on the subclass is updated, so is the alias here
>> >         """
>> >         self.alias = value
>> >
>> > class Subclass(Superclass):
>> >     def __init__(self, x):
>> >         self.x = x
>> >         Superclass.__init__(self, self.x)
>> >
>> >     def __repr__(self):
>> >         return "x: %s\nalias: %s" % (self.x, self.alias)
>> >
>> >
>> > if __name__ == "__main__":
>> >     foo = Subclass(1)
>> >     print foo.alias
>> >
>> >     foo.x = 6
>> >     # Should return 6 !!!
>> >     print foo.alias
>> >
>> > </pre>
>>
>> ISTM the easiest way would be to define a property on the superclass:
>>
>> class Superclass(object):
>>     @property
>>     def alias(self):
>>         return self.x
>>
>> Whatever happens, self.alias will be identical to self.x. Is that what
>> you're after?
>>
>> ChrisA
>
> Yes, but that doesn't seem to work.  It looks like there is a way to do it if you make the original value a list (mutable) instead of an integer.  I really need to do it with an arbitrary object.  Not sure if I can hack the list trick to work in my case though.

What about it doesn't work? Did you want to be able to set the value
via the alias as well? Then use a property with a setter:

class Superclass(object):
    @property
    def alias(self):
        return self.x

    @alias.setter
    def alias(self, value):
        self.x = value