[Numpy-discussion] Subclassing numarray arrays
jmiller at stsci.edu
Thu Sep 25 12:06:02 CDT 2003
On Thu, 2003-09-25 at 12:28, Paul Dubois wrote:
> I have not followed this thread in any detail but I continue to be
> puzzled by the idea of subclassing numarray arrays. Any subclass worth
> its salt has an unpredictable constructor argument list, so that
> virtually every ufunc and every array method have to be overridden in
> order to return the subclass object rather than a numarray.
I think there is a need to effectively subclass numarray where the
parameter lists don't change. Doing a Matrix subclass sounds reasonable
to me and we should explore the OOP necessary to make it convenient.
STSCI hasn't asked for it, but a couple different numarray contributors
> I gather
> that the defers-to-me stuff allows the subclass to get control of a
> mixed operation but that was possible with the radd, etc. operators
> already as in the old MA.
radd does not work for numarray + MA. Instead, the expression is
resolved as numarray.__add__(MA). Were MA a numarray subclass, it would
work, given the facilities provided by Python alone.
The defers-to-me-stuff is a simple work around to avoid having to
reverse engineer this one Numeric behavior.
> This reasoning led me to believe that subclassing had virtually no value
> and to the design of MA that has-a numeric array rather than is-a.
Since we want to port MA as-is to numarray, we're not changing that.
> Is there some big breakthrough here I missed?
No, but there are two issues: (1) effectively supporting subclasses
(2) effectively supporting interoperability with other classes.
(1) needs more discussion.
(2) is already solved.
Todd Miller jmiller at stsci.edu
STSCI / ESS / SSB
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