[Numpy-discussion] Psyco MA?

Paul F Dubois paul at pfdubois.com
Fri Feb 7 16:29:02 CST 2003


Just to confirm the obvious, I don't know the difference between Psyco and
Pyrex and if I ever did it is Friday night and I've lost it. Any two words
that share two letters look the same to me right now. 



> -----Original Message-----
> From: numpy-discussion-admin at lists.sourceforge.net 
> [mailto:numpy-discussion-admin at lists.sourceforge.net] On 
> Behalf Of Tim Hochberg
> Sent: Friday, February 07, 2003 3:09 PM
> To: Chris Barker
> Cc: Paul F Dubois; numpy-discussion at lists.sourceforge.net
> Subject: Re: [Numpy-discussion] Psyco MA?
> 
> 
> Chris Barker wrote:
> 
> >oops, sorry about the blank message.
> >
> >Paul F Dubois wrote:
> >  
> >
> >>{ CC to GvR just to show why I'm +1 on the if-PEP. I liked this in 
> >>another
> >>    
> >>
> >
> >What the heck is the if-PEP ?
> >  
> >
> 
> Pep 308. It's stirring up a bit of a ruckos on CLP as we speak.
> 
> >>Perhaps knowlegeable persons could comment on the feasibility of 
> >>coding MA (masked arrays) in straight Python and then using 
> Psyco on 
> >>it?
> >>    
> >>
> >
> >Is there confusion between Psyco and Pyrex? Psyco runs regular old 
> >Python bytecode, and individually compiles little pieces of it as 
> >needed into machine code. AS I understand it, this should make loops 
> >where the inner part is a pretty simple operation very fast.
> >
> >However, Psyco is pretty new, and I have no idea how robust 
> and stable, 
> >but certainly not cross platform. As it generates machine code, it 
> >needs to be carefully ported to each hardware platform, and it 
> >currently only works on x86.
> >  
> >
> Psyco seems fairly stable these days. However it's one of 
> those things 
> that probably needs to get a larger cabal of users to shake 
> the bugs out 
> of it. I still only use it to play around with because all 
> things that I 
> need speed from I end up doing in Numeric anyway.
> 
> >Pyrex, on the other hand, is a "Python-like" language that 
> is tranlated 
> >into C, and then the C is compiled. It generates pretty darn 
> platform 
> >independent, so it should be able to be used on all platforms.
> >
> >
> >In regard to your question about MA (and any ther similar 
> project): I 
> >think Psyco has the potential to be the next-generation Python VM, 
> >which will have much higher performance, and therefore 
> greatly reduce 
> >the need to write extensions for the sake of performance. I supsect 
> >that it could do its best with large, multi-dimensional arrays of 
> >numbers if there is a Python native object of such a type. Psycho, 
> >however is not ready for general use on all platforms, so in the 
> >forseeable future, there is a need for other ways to get decent 
> >performance. My suggestion follows:
> >
> >  
> >
> >>It could have been written a lot simpler if performance 
> didn't dictate 
> >>trying to leverage off Numeric. In straight Python one can 
> imagine an 
> >>add, for example, that was roughly:
> >>    for k in 0<= k < len(a.data):
> >>       result.mask[k] = a.mask[k] or b.mask[k]
> >>       result.data[k] = a.data[k] if result.mask[k] else 
> a.data[k] + 
> >>b.data[k]
> >>    
> >>
> >
> >This looks like it could be written in Pyrex. If Pyrex were suitably 
> >NumArray aware, then it could work great.
> >
> >What this boils down to, in both the Pyrex and Psyco 
> options, is that 
> >having a multi-dimensional homogenous numeric data type that is 
> >"Native" Python is a great idea! With Pyrex and/or Psyco, Numeric3 
> >(NumArray2 ?) could be implimented by having only the 
> samallest core in 
> >C, and then rest in Python (or Pyrex)
> >  
> >
> For Psyco at least you don't need a multidimensional type. 
> You can get 
> good results with flat array, in particular array.array. The number I 
> posted earlier showed comparable performance for Numeric and a 
> multidimensional array type written all in python and psycoized.
> 
> And since I suspect  that I'm the mysterious person who's name Paul 
> couldn't remember, let me say I suspect the MA would be faster in 
> psycoized python than what your doing now as long as a.data was an 
> instance of array.array. However, there are at least three problems. 
> Psyco doesn't fully support the floating point type('f') right now 
> (although it does support most of the various  integral types in 
> addition to 'd'). I assume that these masked arrays are 
> multidimensional, so someone would have to build the basic 
> multidimensional machinery around array.array to make them 
> work. I have 
> a good start on this, but I'm not sure when I'm going to have time to 
> work on this more. The biggy though is that psyco only works on x86 
> machines.  What we really need to do is to clone Armin.
> 
> >While the Psyco option is the rosy future of Python, Pyrex 
> is here now, 
> >and maybe adopting it to handle NumArrays well would be easier than 
> >re-writing a bunch of NumArray in C.
> >  
> >
> This sounds like you're conflating two different issues. The 
> first issue 
> is that Numarray is relatively slow for small arrays.  Pyrex 
> may indeed 
> be an easier way to attack this although I wouldn't know, I've only 
> looked at it not tried to use it. However, I think that this is 
> something that can and should wait. Once use cases of numarray being 
> _too_ slow for small arrays start piling up, then it will be time to 
> attack the overhead. Premature optimization is the root of 
> all evil and 
> all that.
> 
> The second issue is how to deal with code that does not 
> vectorize well. 
> Here Pyrex again might help if it were made Numarray aware. However, 
> isn't this what scipy.weave already does? Again, I haven't 
> used weave, 
> but as I understand it, it's another python-c bridge, but one that's 
> more geared toward numerics stuff.
> 
> 
> -tim
> 
> 
> 
> 
> 
> 
> 
> 
> 
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