[Numpy-discussion] possible bug: __array_wrap__ is not called during arithmetic operations in some cases

Darren Dale dsdale24@gmail....
Sun Feb 22 17:35:47 CST 2009


On Sun, Feb 22, 2009 at 6:28 PM, Pierre GM <pgmdevlist@gmail.com> wrote:

>
> On Feb 22, 2009, at 6:21 PM, Eric Firing wrote:
>
> > Darren Dale wrote:
> >> Does anyone know why __array_wrap__ is not called for subclasses
> >> during
> >> arithmetic operations where an iterable like a list or tuple
> >> appears to
> >> the right of the subclass? When I do "mine*[1,2,3]", array_wrap is
> >> not
> >> called and I get an ndarray instead of a MyArray. "[1,2,3]*mine" is
> >> fine, as is "mine*array([1,2,3])". I see the same issue with
> >> division,
> >
> > The masked array subclass does not show this behavior:
>
> Because MaskedArray.__mul__ and others are redefined.
>
> Darren, you can fix your problem by redefining MyArray.__mul__ as:
>
>     def __mul__(self, other):
>         return np.ndarray.__mul__(self, np.asanyarray(other))
>
> forcing the second term to be a ndarray (or a subclass of). You can do
> the same thing for the other functions (__add__, __radd__, ...)


Thanks for the suggestion. I know this can be done, but ufuncs like
np.multiply(mine,[1,2,3]) will still not work. Plus, if I reimplement these
methods, I take some small performance hit. I've been putting a lot of work
in lately to get quantities to work with numpy's stock ufuncs.

Darren
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