Here's a PR with a different dicsussion of __array__: https://github.com/numpy/numpy/pull/14529
-CHB On Mon, Sep 16, 2019 at 3:23 PM Chris Barker <chris.bar...@noaa.gov> wrote: > OK -- I *finally* got it: > > when you pass an arbitrary object into np.asarray(), it will create an > array object scalar with the object in it. > > So yes, I can see that you may want to raise a TypeError instead, so that > users don't get an object array scalar when they wre expecting to get an > array-like object. > > So it's probably a good idea to recommend that when a class implements > __dauckarray__ that it also implements __array__, which can either raise an > exception or return and ndarray. > > -CHB > > > On Mon, Sep 16, 2019 at 3:11 PM Chris Barker <chris.bar...@noaa.gov> > wrote: > >> On Mon, Sep 16, 2019 at 2:27 PM Stephan Hoyer <sho...@gmail.com> wrote: >> >>> On Mon, Sep 16, 2019 at 1:45 PM Peter Andreas Entschev < >>> pe...@entschev.com> wrote: >>> >>>> What would be the use case for a duck-array to implement __array__ and >>>> return a NumPy array? >>> >>> >> >>> Dask arrays are a good example. They will want to implement >>> __duck_array__ (or whatever we call it) because they support duck typed >>> versions of NumPy operation. They also (already) implement __array__, so >>> they can converted into NumPy arrays as a fallback. This is convenient for >>> moderately sized dask arrays, e.g., so you can pass one into a matplotlib >>> function. >>> >> >> Exactly. >> >> And I have implemented __array__ in classes that are NOT duck arrays at >> all (an image class, for instance). But I also can see wanting to support >> both: >> >> use me as a duck array >> and >> convert me into a proper numpy array. >> >> OK -- looking again at the NEP, I see this suggested implementation: >> >> def duckarray(array_like): >> if hasattr(array_like, '__duckarray__'): >> return array_like.__duckarray__() >> return np.asarray(array_like) >> >> So I see the point now, if a user wants a duck array -- they may not want >> to accidentally coerce this object to a real array (potentially expensive). >> >> but in this case, asarray() will only get called (and thus __array__ will >> only get called), if __duckarray__ is not implemented. So the only reason >> to impliment __array__ and raise and Exception is so that users will get >> that exception is the specifically call asarray() -- why should they get >> that?? >> >> I'm working on a PR with suggestion for this. >> >> -CHB >> >> -- >> >> Christopher Barker, Ph.D. >> Oceanographer >> >> Emergency Response Division >> NOAA/NOS/OR&R (206) 526-6959 voice >> 7600 Sand Point Way NE (206) 526-6329 fax >> Seattle, WA 98115 (206) 526-6317 main reception >> >> chris.bar...@noaa.gov >> > > > -- > > Christopher Barker, Ph.D. > Oceanographer > > Emergency Response Division > NOAA/NOS/OR&R (206) 526-6959 voice > 7600 Sand Point Way NE (206) 526-6329 fax > Seattle, WA 98115 (206) 526-6317 main reception > > chris.bar...@noaa.gov > -- Christopher Barker, Ph.D. Oceanographer Emergency Response Division NOAA/NOS/OR&R (206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception chris.bar...@noaa.gov
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