[Python-Dev] Bad interaction of __index__ and sequence repeat

[Guido van Rossum]

All, please decide without me.

On 8/1/06, Nick Coghlan <ncoghlan at gmail.com> wrote:
> Nick Coghlan wrote:
> > Travis Oliphant wrote:
> >>> Probably the most interesting thing now would be for Travis to review
> >>> it, and see whether it makes things easier to handle for the Numeric
> >>> scalar types (given the amount of code the patch deleted from the
> >>> builtin and standard library data types, hopefully the benefits to
> >>> Numeric will be comparable).
> >>
> >> I noticed most of the checks for PyInt where removed in the patch.  If I
> >> remember correctly, I left these in for "optimization."   Other than
> >> that, I think the patch is great.
> >
> > You're right - there was a fast path based on PyInt_Check in
> > _PyEval_SliceIndex that got lost, which I'll add back in. I'll also add
> fast
> > paths for PyInt_Check to the functions in abstract.c, too.
> >
> > The other PyInt_Check's (in slot_nb_index and instance_index) were there
> to
> > check that __index__ returned the right thing. The check was still there
> in
> > slot_nb_index, but I'd incorrectly removed it from instance_index. I'll
> add
> > that one back in, too.
> >
> > Once that's done, I'll update the tracker item and reassign to Tim for a
> review.
>
> Aside from the 'assign to Tim' part, this is done now (pep357-fix-v3 on the
> tracker item). I also tweaked the clipping version of the C API to
> optionally
> expose the overflow flag that abstract.c was using internally so the client
> code can find out whether or not clipping actually occurred.
>
> The patch also updates the index unit tests to:
>    - cover the various type errors that Travis picked up
>    - actually run the full set of unit tests under -O
>    - only run the basic sequence independent tests once (instead of once per
> sequence type)
>
> Neal also had a number of questions that I responded to in the tracker
> comments.
>
> The most significant question related to the API signature, which Neal
> considered potentially confusing:
>    PyNumber_Index(PyObject *item, int *is_index)
>
> I added the is_index flag to the function signatures instead of providing a
> separate PyNumber_IndexCheck function in order to avoid doing the same type
> check twice in the typical mp_subscript implementation cases.
>
> One possibility would be to invert the sense of that flag and call it
> "typeerror", which probably more accurately reflects what it's intended for
> -
> it's a way of telling the function "if this object does not have the correct
> type, tell me by setting this flag instead of by setting the Python error
> state".
>
> Regards,
> Nick.
>
> --
> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
> ---------------------------------------------------------------
>              http://www.boredomandlaziness.org
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-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)