Thanks for the response, Sebastian! I'll keep an eye out on that repo. Should there be (is there already) a link to it from the docs?
On Tue, 30 May 2023, at 6:21 PM, Sebastian Berg wrote: > On Mon, 2023-05-29 at 10:55 +1000, Juan Nunez-Iglesias wrote: >> Hi folks, >> >> Apologies if this is documented somewhere, but I haven't been able to >> find it. I've read through NEP-42 [1] and skimmed NEP-41 [2], but I'm >> not sure: >> >> (a) at what point of implementation we are, and >> (b) if it's pretty much done, *how* to define a custom categorical >> dtype. >> >> In my use case, I'd need a dtype that is implemented as some int >> scalar where only certain values are allowed, ie the NumPy equivalent >> of: >> >> class Label(Enum) >> CAR = 1 >> DOG = 45 >> NULL = 255 >> >> But with the ability to specify that I only need a uint8 in this >> case. >> >> Is that possible today using Python (no C/Cython) and if so, is there >> some documentation or user example or StackOverflow answer that shows >> how to do this? If not, is it a design goal of the NEPs to allow such >> a thing? (I can be patient 😂) > > > The NEP is pretty far along and we have some examples of use here: > https://github.com/numpy/numpy-user-dtypes > > There are still kinks to be iron out thouh and nobody has tried a > "categorical" type functionality yet. > > However, without C/Cython it is not possible at this time. What we need > is a Categorical or Enum DType implemented in C, which would then allow > creating the specific `LabelDType` in Python. [1] > > On the other hand, writing that single C implementation for a minimal > `IntEnum` DType factory is likely quite reasonably scoped. > (As a prototype implementation, but I expect adapting to a final > version should be smooth.) > > - Sebastian > > > [1] Maybe as a DType factory in C to create arbitrary `IntEnum` likes, > maybe as parametric DType. I suspect the first is the right way, it may > be tedious or even very hard right now, that is a kink that needs > ironing out eventually. Python 3.12 has some fixes around Metaclass > instantiation in C (with backcompat hacks) which hopefully make this > less of a drain on sanity. > > >> >> Thank you! >> >> Juan. >> >> [1]: https://numpy.org/neps/nep-0042-new-dtypes.html >> [2]: https://numpy.org/neps/nep-0041-improved-dtype-support.html >> _______________________________________________ >> NumPy-Discussion mailing list -- numpy-discussion@python.org >> To unsubscribe send an email to numpy-discussion-le...@python.org >> https://mail.python.org/mailman3/lists/numpy-discussion.python.org/ >> Member address: sebast...@sipsolutions.net > > > > _______________________________________________ > NumPy-Discussion mailing list -- numpy-discussion@python.org > To unsubscribe send an email to numpy-discussion-le...@python.org > https://mail.python.org/mailman3/lists/numpy-discussion.python.org/ > Member address: j...@fastmail.com _______________________________________________ NumPy-Discussion mailing list -- numpy-discussion@python.org To unsubscribe send an email to numpy-discussion-le...@python.org https://mail.python.org/mailman3/lists/numpy-discussion.python.org/ Member address: arch...@mail-archive.com
