[Numpy-discussion] Just ignore me. That was an accidental send.

Todd Miller jmiller at stsci.edu
Fri Feb 4 06:07:05 CST 2005


Please ignore that last post.   It consists of unfinished thoughts which
were sent accidentally.  Doing numarray isn't easy.

Regards,
Todd

On Fri, 2005-02-04 at 07:24, Todd Miller wrote:
> On Thu, 2005-02-03 at 14:28 -0700, Travis Oliphant wrote:
> > 
> > I fixed a major oversight in Numeric3 and now it works pretty well (it 
> > is basically old Numeric with a bunch of new types, no math (yet)), 
> > using new-style classes, and some checks for alignment when 
> > dereferencing data.
> > 
> > I did some simple array creation timing tests.  An example of the 
> > results is given below.  The bottom line is that new-style classes do 
> > nothing but speed up (a little bit) basic object creation. 
> 
> I think you've done a real service here,  bounding the cost of new-style
> classes,  but I'm not convinced we have a bottom line,  at least not in
> the sense of my own FUD about new style classes.  I'm not contesting the
> technical direction you're taking with Numeric3 (I hope it works,  but
> the details are up to you),  but I am contesting the idea that new style
> classes do nothing but speed up object creation.
> 
> I think among the promises of new style classes are the ability to
> subclass in both C and Python,  and my thinking is that if you actually
> do *that*,  you pay for it through the nose.  So,  I'm trying to dispell
> the notion that new style classes are pure bliss;  I think they need to
> be used either with insight (say a lot more than C++ OOP) or sidestepped
> altogether (as, IMHO, you have done).  Using them,  you're up against
> more than just faking OOP in C.
> 
> I think one of the flaws currently in numarray is that I tried to push a
> Python class hierarchy down (or half-way down) into C.   IMO,  that's
> where some of the cost of new style classes would be incurred.  The cost
> of the object __dict__ I mostly expected to be optimized out,  perhaps
> by freelist magic or some lazy construction technique.  If it's the
> latter.
> 
> As far as state in the arrayobject goes, I *did* flatten the numarray
> class heirarchy.  But I didn't flatten the numarray class hierarchy in
> terms of constructors and methods,  and my sense is that there is a
> significant cost there.   Calling up the class hierarchy uses Python
> method calls (maybe an error) which themselves require the construction,
> parsing, and destruction of tuple objects and at least some of the
> objects the tuples contain.  
> 
> So,  I'd assert that unless you solve *that* problem,  using new style
> classes and some form of inheritance,  saying that new style classes do
> nothing but speed things up is stretching the truth.  To really disprove
> the hidden costs in my FUD,  I'd want to see a C basetype and
> inheritance by a Python subclass.
> 
> If you actually use them for anything,  I think you wind up paying
> Python function call overheads.  That, anyway,  is a problem to solve
> (or sidestep as you have done) for numarray.
> 
> AFICT, among the things you're doing with Numeric3 (which I applaud) is
> basically throwing out inheritance from the fundamental array type;
> squashing all the constructor functionality for NDArray and NumArray
> into one type was more than I had the nerve to do.  So, I know you're
> adding the ability to subclass,  but you're not actually using it,  so I
> think it's stretching the truth to say it speeds things up.
> 
> In numarray,  we use it,  in both C and Python,  and that's maybe not a
> good thing.  
> 
> If you can pull it off and still cleanly support the features of
> numarray,  it will be a triumph of KISS.  But that's not a given.
> 
> 
> 
> 
> 
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