[Numpy-discussion] subclassing matrix

Basilisk96 basilisk96@gmail....
Sat Jan 12 15:24:31 CST 2008


On Jan 12, 1:36 am, "Timothy Hochberg" <tim.hochb...@ieee.org> wrote:
> I believe that you need to look at __array_finalize__ and __array_priority__
> (and there may be one other thing as well, I can't remember; it's late).
> Search for __array_finalize__ and that will probably help get you started.
>

Well sonovagun!
I removed the hack.
Then just by setting __array_priority__ = 20.0 in the class body,
things are magically working almost as I expect. I say "almost"
because of this custom method:

    def cross(self, other):
        """Cross product of this vector and another vector"""
        return _N.cross(self, other, axis=0)

That call to numpy.cross returns a numpy.ndarray. Unless I do return
Vector(_N.cross(self, other, axis=0)), I get problems downstream.

When is __array_finalize__ called? By adding some print traces, I can
see it's called every time an array is modified in any way i.e.,
reshaped, transposed, etc., and also during operations like u+v, u-v,
A*u. But it's not called during the call to numpy.cross. Why?

Cheers,
-Basilisk96


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