[Python-Dev] subclassing builtin data structures (original) (raw)

Ethan Furman ethan at stoneleaf.us
Fri Feb 13 04:00:41 CET 2015

On 02/12/2015 06:57 PM, Steven D'Aprano wrote:

On Thu, Feb 12, 2015 at 06:14:22PM -0800, Ethan Furman wrote:

On 02/12/2015 05:46 PM, MRAB wrote:

On 2015-02-13 00:55, Guido van Rossum wrote:

Actually, the problem is that the base class (e.g. int) doesn't know how to construct an instance of the subclass -- there is no reason (in general) why the signature of a subclass constructor should match the base class constructor, and it often doesn't.

So this is pretty much a no-go. It's not unique to Python -- it's a basic issue with OO. Really? What I was asking about, and Guido responded to, was not having to specifically override add, mul, sub, and all the others; if we do override them then there is no problem. I think you have misunderstood MRAB's comment. My interpretation is that MRAB is suggesting that methods in the base classes should use type(self) rather than hard-coding their own type.

That makes more sense, thanks.

-- Ethan

-------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 836 bytes Desc: OpenPGP digital signature URL: <http://mail.python.org/pipermail/python-dev/attachments/20150212/c7c87f45/attachment.sig>

More information about the Python-Dev mailing list