[Python-Dev] NotImplemented reaching top-level (original) (raw)
Armin Rigo arigo at tunes.org
Mon Dec 26 17:27:10 CET 2005
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Hi,
On Mon, Dec 26, 2005 at 02:40:38AM +1000, Nick Coghlan wrote:
That sounds like the right definition to me (I believe this behaviour is what Raymond and Facundo were aiming for with the last round of updates to Decimal).
Done in patch #1390657.
Although this patch passes all existing tests plus the ones it adds, there is a corner and untested case where it could potentially break code. Indeed, the only sane patch I could come up with makes user-defined types fail to work with PySequence_Concat() and PySequence_Repeat() -- details in the patch. So I propose that we clarify what these two functions really mean in term of the Python language spec, instead of just in term of the CPython-specific sq_concat and sq_repeat slots. (BTW that's needed for PyPy/Jython/etc., too, to give a reasonable meaning to the operator.concat() and operator.repeat() built-ins.)
I propose the following definitions (which are mostly what the docstrings already explain anyway):
PySequence_Concat(a, b) and operator.concat(a, b) mean "a + b", with the difference that we check that both arguments appear to be sequences (as checked with operator.isSequenceType()).
PySequence_Repeat(a, b) and operator.repeat(a, b) mean "a * b", where "a" is checked to be a sequence and "b" is an integer. Some bounds can be enforced on "b" -- for CPython, it means that it must fit in a C int.
The idea is to extend PySequence_Concat() and PySequence_Repeat() to match the above definitions precisely, which means that for objects not defining sq_repeat or sq_concat but still appearing to be sequences, nb_add and nb_multiply should be tried. I don't think that this would break existing C or Python code, but it should probably only go in 2.5, together with the patch #1390657 that relies on it.
A bientot,
Armin
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