[Numpy-discussion] asanyarray vs. asarray
chris.barker at noaa.gov
Tue Oct 30 17:44:48 EDT 2018
On Tue, Oct 30, 2018 at 2:22 PM, Stephan Hoyer <shoyer at gmail.com> wrote:
> The Liskov substitution principle (LSP) suggests that the set of
> reasonable ndarray subclasses are exactly those that could also in
> principle correspond to a new dtype. Of np.ndarray subclasses in
> wide-spread use, I think only the various "array with units" types come
> close satisfying this criteria. They only fall short insofar as they
> present a misleading dtype (without unit information).
How about subclasses that only add functionality? My only use case of
subclassing is exactly that:
I have a "bounding box" object (probably could have been called a
rectangle) that is a subclass of ndarray, is always shape (2,2), and has
various methods for merging two such boxes, etc, adding a point, etc.
I did it that way, 'cause I had a lot of code already that simply used a
(2,2) array to represent a bounding box, and I wanted all that code to
I have had zero problems with it.
Maybe that's too trivial to be worth talking about, but this kind of use
case can be handy.
It is a bit awkward to write the code, though -- it would be nice to have a
cleaner API for this sort of subclassing (not that I have any idea how to
The main problem with subclassing for numpy.ndarray is that it guarantees
> too much: a large set of operations/methods along with a specific memory
> layout exposed as part of its public API.
This is a big deal -- we really have two concepts here:
- a Python class (type) with certain behaviors in Python code
- a wrapper around a strided memory block.
maybe it's possible to be clear about that distinction:
"Duck Arrays" are the Python API
Maybe a C-API object would be useful, that shares the memory layout, but
could have completely different functionality at the Python level.
Christopher Barker, Ph.D.
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.Barker at noaa.gov
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the NumPy-Discussion