Alias for an attribute defined in a superclass

Jean-Michel Pichavant jeanmichel at sequans.com
Fri Apr 1 11:54:06 CEST 2011


Raymond Hettinger wrote:
> On Mar 31, 3:14 pm, Ben Finney <ben+pyt... at benfinney.id.au> wrote:
>   
>> Howdy all,
>>
>> I want to inherit from a class, and define aliases for many of its
>> attributes. How can I refer to “the attribute that will be available by
>> name ‘spam’ once this class is defined”?
>>
>>     class Foo(object):
>>         def spam(self):
>>             pass
>>
>>         def eggs(self):
>>             pass
>>
>>     class Bar(Foo):
>>         beans = Foo.spam
>>         mash = Foo.eggs
>>
>> Is that the right way to do it?
>>     
>
> For methods, that will work just fine.  For attributes, you will need
> to make @property accessors that get and set the underlying attribute.
>
>
> Raymond
>   
For attributes you could also override __getattribute__ & __setattr__ to 
wrap Bar's names into Foo's names.
Could work also for methods, but for methods your current idea is much 
more simple.

class Foo(object):
    def __init__(self):
       self.spam = 'someSpam'
       self.eggs = 'fewEggs'

    def vanilla(self):
        return self.spam

class Bar(Foo):
    _map = {
       'beans': 'spam',
       'mash': 'eggs',
       'chocolate': 'vanilla',
    }
    def __getattribute__(self, attribute):
        getSafely = object.__getattribute__
        _map =  getSafely(self, '_map')
        if attribute in _map:
            return getSafely(self, _map[attribute])
        else:
            return getSafely(self, attribute)


Bar().chocolate()
'someSpam'

Bar().mash
'fewEggs'

JM



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