[Python-ideas] Name mangling and code repetition (with cooperative inheritance use case)

[Zahari Petkov]

Thanks for the answer. Now I realize that I picked a wrong example in
the email, and your argument is valid about it. However the code
repetition in the gist is a valid example, it cannot be resolved with
turning the variables/methods to single underscore mode. I actually
almost never use the private convention and I am aware of its purpose
and use cases (e.g. __update = update after definition).

I will think a bit further for a different not-confusing example and write back.

Best,
Zahari


On Tue, Apr 9, 2013 at 2:15 AM, Guido van Rossum <guido at python.org> wrote:
> You are misunderstanding __private. It is for use *within one class*
> only. For your purpose you should use single underscore (sometimes
> known as "protected").
>
> On Mon, Apr 8, 2013 at 4:11 PM, Zahari Petkov <zarchaoz at gmail.com> wrote:
>> Hello everyone,
>>
>> In a certain implementation where I was doing some form of dispatch using
>> composition, I decided to try out cooperative inheritance with super. However,
>> I stumbled at something unexpected - there was nothing wrong with cooperative
>> inheritance with super, but the implementation started to have repetative
>> code, which could not be easily resolved, because of how name mangling of
>> private attribute works.
>>
>> In short my proposal is for a language feature or mechanism, which will allow
>> automatic redefinition of methods through the descendants of a superclass
>> during compilation time - at the same time name unmangling is done. In the
>> example below I use a decorator - just to illustrate the idea in a very simple
>> way:
>>
>>
>> class A:
>>     __val = 'a'
>>
>>     @propagate_through_descendants
>>     def print_val(self):
>>         print(self.__val)
>>
>>
>> class B(A):
>>     __val = 'b'
>>
>>
>> b = B()
>> b.print_val()
>>
>>
>> Please, check the following gist for a bit more concrete example (short and
>> working) with cooperative inheritance:
>>
>> https://gist.github.com/majorz/5341333
>>
>> The code duplication is very obvious and unavoidable (the two __call__
>> methods have exactly the same code, which cannot be moved to the superclass).
>> I tried some metaprogramming, but even then it was hard to resolve, since
>> name unmangling seems to happen during complilation time as far as I
>> understand.
>>
>> Thanks,
>> Zahari
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>
>
>
> --
> --Guido van Rossum (python.org/~guido)