[Numpy-discussion] is __array_ufunc__ ready for prime-time?

[Stephan Hoyer]

On Thu, Nov 2, 2017 at 12:42 PM Nathan Goldbaum <nathan12343 at gmail.com>
wrote:

> Would this issue be ameliorated given Nathaniel's proposal to try to move
> away from subclasses and towards storing data in dtypes? Or would that just
> mean that xarray would need to ban dtypes it doesn't know about?
>

Yes, I think custom dtypes would definitely help. Custom dtypes have a well
contained interface, so lots of operations (e.g., concatenate, reshaping,
indexing) are guaranteed to work in a dtype independent way. If you try to
do an unsupported operation for such a dtype (e.g., np.datetime64), you
will generally get a good error message about an invalid dtype.

In contrast, you can overload a subclass with totally arbitrary semantics
(e.g., np.matrix) and of course for duck-types as well.

This makes a big difference for libraries like dask or xarray, which need a
standard interface to guarantee they do the right thing. I'm pretty sure we
can wrap a custom dtype ndarray with units, but there's no way we're going
to support np.matrix without significant work. It's hard to know which is
which without well defined interfaces.
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