Thanks! I understand your hesitation; certainly if I am using undocumented APIs (or even if they are otherwise unused) I understand that it will be on my shoulders to preserve compatibility if you change things. But I would definitely like to get basic functionality working with current (and older, to be honest) NumPy versions.
Ah, I missed previously that the array objects are passed as the void* args to the PyArray_VectorUnaryFunc. But it's documented here. https://docs.scipy.org/doc/numpy-1.13.0/reference/c-api.types-and-structures.html#c.PyArray_ArrFuncs.cast (Why aren't these two args PyArrayObject* then?) As far as I can tell, get_datetime_metadata_from_dtype() isn't a public API? It certainly isn't spelled like one. It's declared in numpy/core/src/multiarray/_datetime.h, which doesn't appear to be #included in any other header. I suppose I could duplicate the struct layout in my own code to fish out the field I need. Obviously, compatibility is my own problem then. Regards, Alex On Mon, May 13, 2019, at 01:31, Sebastian Berg wrote: > Hi Alex, > > On Mon, 2019-05-13 at 00:35 -0400, Alex Samuel wrote: > > Hi, > > > > When registering a custom cast function from datetime64 to another > > dtype, how can I get the units? > > > > I am calling PyArray_RegisterCastFunc from NPY_DATETIME. Ideally, > > I'd like to register a separate cast function for each datetime64 > > units (or none at all... I don't want all units to be castable). > > Next best thing would be to obtain the units in the cast function and > > dispatch accordingly. > > > > Is this possible? I glanced through the code, and it looks like > > there's a lot of hard-coded logic around datetime64, but I didn't go > > through it carefully. Thought I'd ask before drilling further down. > > get_datetime_metadata_from_dtype > > No, I do not think that is possible. But you do get the array pointers > during the cast. I honestly would prefer not to promise that all of > this will survive if we change this in numpy, since there are almost no > users. But I think if we change it I could promise to help with > cleaning it up in ora. > > I think this is public API (but I do not really like anyone using it > ;)), so you can use: > > ``` > /* > * This function returns a pointer to the DateTimeMetaData > * contained within the provided datetime dtype. > */ > static PyArray_DatetimeMetaData * > get_datetime_metadata_from_dtype(PyArray_Descr *dtype) > { > /* original error check for DATETIME unnecessary for you */ > return &(((PyArray_DatetimeDTypeMetaData *)dtype->c_metadata)->meta); > } > ``` > > And in the castfunc (fromarr is passed in as a void * as far as): > ``` > NPY_DATETIMEUNIT base = get_datetime_metadata_from_dtype( > PyArray_DESCR(fromarr))->base; > ``` > > Where NPY_DATETIMEUNIT is the enum defined in ndarraytypes.h. The logic > will have to happen inside the cast func. > > I would hope there was a better way, but I cannot think of any, and I > am scared that supporting this will add yet another ugly hack when we > want to improve dtypes... > > Best, > > Sebastian > > > > > Thanks in advance, > > Alex > > > > > > _______________________________________________ > > NumPy-Discussion mailing list > > NumPy-Discussion@python.org > > https://mail.python.org/mailman/listinfo/numpy-discussion > > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@python.org > https://mail.python.org/mailman/listinfo/numpy-discussion > > > *Attachments:* > * signature.asc
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