Guido van Rossum <gu...@python.org> added the comment: > Why did the list implementation get changed in Py3.x?
Because we decided to get rid of the sq_slice and sq_ass_slice slots in PySequenceMethods, and that in turn was because we got rid of the slice-related opcodes and the separate __getslice__ and __setslice__ magic methods. > Is it now necessary for any subscripting type to put the same method > in both the sequence methods and mapping methods? Yes, if the type wants to support slicing. The reason is that while we changed many things, we didn't want to change the signature of the methods that we kept, and the sq_item/sq_ass_item signatures have arguments that make it impossible to pass the info necessary for a slice. > Was this change necessary? The changes are briefly mentioned in PEP 3100 without any motivation. However I think the rationale was the observation that the old sq_slice / sq_ass_slice took only integers (really ssize_t), meaning that it was impossible to implement a sequence type taking a slice with arguments outside the range supported by ssize_t (e.g. a custom range type supporting huge longs). Or with non-integral arguments. This problem never existed for non-slice __get__ since one could always implement mp_subscript / mp_ass_subscript. Was it necessary? I'm not sure -- but that's water under the bridge. Was it a good change? From the POV of Python code, yes. The old approach caused some odd problems for classes implementing __getslice__ / __setslice__ (since those were invoked after the arguments had been pushed through the sq_slice / sq_ass_slice API). > Personally, I think PyMapping_Check and PySequence_Check should be > deprecated and removed. Like their Python counterparts, > operator.isMappingType() and operation.isSequenceType(), they are > unreliable at best in the face of not LBYL and abcs. Right, calling PyMapping_Check() was never particularly reliable, and extension modules depending on it probably always had subtle bugs. Perhaps it would be nice if we provided a C API to at least some of the ABC package. ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue5945> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
