On Sat, Feb 24, 2018 at 5:24 AM, Chris Barker <chris.bar...@noaa.gov> wrote: > On Thu, Feb 22, 2018 at 6:21 PM, Nick Coghlan <ncogh...@gmail.com> wrote: >> >> > (I wonder if the discrepancy is due to some internal interface that >> > loses >> > the distinction between None and 1 before the decision is made whether >> > to >> > use advanced slicing or not. But that's a possible explanation, not an >> > excuse.) >> >> That explanation seems pretty likely to me, as for the data types >> implemented in C, we tend to switch to the Py_ssize_t form of slices >> pretty early, and that can't represent the None/1 distinction. >> >> Even for Python level collections, you lose the distinction as soon as >> you call slice.indices (as that promises to return 3-tuple of >> integers). > > > If this is the case -- backward compatibility issues aside, wouldn't it be > very hard to fix? > > Which means that should be investigated before going to far down the "how > much code might this break" route. > > And certainly before adding a Deprecation Warning.
Ignoring backward compatibility, it ought to be possible to (ab)use a stride of zero for this. Calling slice.indices() on something with a stride of zero raises ValueError, so there's no ambiguity. But it would break code that iterates in a simple and obvious way, and (ugh ugh) break it in a very nasty way: an infinite loop. I'm not happy with that kind of breakage, even with multiple versions posting a warning. In the C API, there's PySlice_GetIndices "[y]ou probably do not want to use this function" and PySlice_GetIndicesEx, the "[u]sable replacement". Much as I dislike adding *yet another* function to do basically the same job, I think that might be the less-bad way to do this. ChrisA _______________________________________________ Python-ideas mailing list Pythonemail@example.com https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/