Op 16-04-13 18:49, Terry Jan Reedy schreef: > On 4/16/2013 5:07 AM, Antoon Pardon wrote: >> Op 16-04-13 05:17, Terry Jan Reedy schreef: >> >>> I will keep the above in mind if I write or review a patch. here are 4 >>> non-subclassable builtin classes. Two are already documented. Bool in >>> one, forget which other. I believe it was recently decided to leave >>> the other two as is given the absence of any practical use case. >> >> Why should there be a practical use case here? > > As a practical matter, the change is non-trivial. Someone has to be > motivated to write the patch to enable subclassing, write tests, and > consider the effect on internal C uses of slice and stdlib Python used > of slice (type() versus isinstance). I see. It seems I have underestimated the work involved.
>> I once had an idea of a slice-like class that I would have liked to >> experiment with. > > Did the idea actually require that instances *be* a slice rather than > *wrap* a slice? As far as I remember I wanted my slice object usable to slice lists with. But python doesn't allow duck typing when you use your object to "index" a list. No matter how much your object resembles a slice, when you actualy try to use it to get a slice of a list, python throw a TypeError with the message "object cannot be interpreted as an index". This in combination with slice not being subclassable effectively killed the idea. As I already said I don't know if the idea would have turned up something usefull. The following years I never had the feeling how great it would have been should I have been able to pursue this idea. I just thought it was a pity I was so thoroughly stopped at the time. -- Antoon Pardon -- http://mail.python.org/mailman/listinfo/python-list