On Tue, Sep 29, 2015 at 2:16 PM, Nathaniel Smith <n...@pobox.com> wrote:
> On Sep 29, 2015 8:25 AM, "Anne Archibald" <archib...@astron.nl> wrote: > > > > IEEE 754 has signum(NaN)->NaN. So does np.sign on floating-point arrays. > Why should it be different for object arrays? > > The argument for doing it this way would be that arbitrary python objects > don't have a sign, and the natural way to implement something like > np.sign's semantics using only the "object" interface is > > if obj < 0: > return -1 > elif obj > 0: > return 1 > elif obj == 0: > return 0 > else: > raise > > In general I'm not a big fan of trying to do all kinds of guessing about > how to handle random objects in object arrays, the kind that ends up with a > big chain of type checks and fallback behaviors. Pretty soon we find > ourselves trying to extend the language with our own generic dispatch > system for arbitrary python types, just for object arrays. (The current > hack where for object arrays np.log will try calling obj.log() is > particularly horrible. There is no rule in python that "log" is a reserved > method name for "logarithm" on arbitrary objects. Ditto for the other > ufuncs that implement this hack.) > > Plus we hope that many use cases for object arrays will soon be supplanted > by better dtype support, so now may not be the best time to invest heavily > in making object arrays complicated and powerful. > > OTOH sometimes practicality beats purity, and at least object arrays are > already kinda cordoned off from the rest of the system, so I don't feel as > strongly as if we were talking about core functionality. > > ...is there a compelling reason to even support np.sign on object arrays? > This seems pretty far into the weeds, and that tends to lead to poor > intuition and decision making. > One of the usecases that has sneaked in during the last few numpy versions is that object arrays contain numerical arrays where the shapes don't add up to a rectangular array. In those cases being able to apply numerical operations might be useful. But I'm +0 since I don't work with object arrays. Josef > -n > > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@scipy.org > https://mail.scipy.org/mailman/listinfo/numpy-discussion > >
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