[Python-Dev] subclassing builtin data structures

[Neil Girdhar]

With Python's cooperative inheritance, I think you want to do everything
through one constructor sending keyword arguments up the chain.  The
keyword arguments are popped off as needed.  With this setup I don't think
you need "overloaded constructors".

Best,
Neil

On Fri, Feb 13, 2015 at 4:44 AM, Jonas Wielicki <j.wielicki at sotecware.net>
wrote:

> If I may humbly chime in this, with a hint...
>
> On 13.02.2015 05:01, Guido van Rossum wrote:
> > On Thu, Feb 12, 2015 at 7:41 PM, Ethan Furman <ethan at stoneleaf.us>
> wrote:
> >> [snip]
> >> 2) always use the type of self when creating new instances
> >>
> >>    pros:
> >>      - subclasses automatically maintain type
> >>      - much less code in the simple cases [1]
> >>
> >>    cons:
> >>      - if constructor signatures change, must override all methods which
> >>        create new objects
> >>
> >> Unless there are powerful reasons against number 2 (such as performance,
> >> or the effort to affect the change), it sure
> >> seems like the nicer way to go.
> >>
> >> So back to my original question: what other concerns are there, and has
> >> anybody done any benchmarks?
> >>
> >
> > Con for #2 is a showstopper. Forget about it.
>
> I would like to mention that there is another language out there which
> knows about virtual constructors (virtual like in virtual methods, with
> signature match requirements and such), which is FreePascal (and Delphi,
> and I think original Object Pascal too).
>
> It is actually a feature I liked about these languages, compared to
> C++03 and others, that constructors could be virtual and that classes
> were first-class citizens.
>
> Of course, Python cannot check the signature at compile time. But I
> think as long as it is documented, there should be no reason not to
> allow and support it. It really is analogous to other methods which need
> to have a matching signature.
>
> just my two cents,
> jwi
>
>
>
>
>
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