[Numpy-discussion] seterr changes

Tim Hochberg tim.hochberg at cox.net
Wed Apr 19 08:58:04 CDT 2006


Hi Travis et al,

I started looking at your seterr changes. I stared at yours for a while 
then I stared at mine for a while. Then I decided that mine wouldn't 
work right in the presence of threads. Then I decided that yours 
wouldn't work right in the presence of threads either. Specifically, it 
looks like ufunc_update_use_defaults isn't going to work. I think I know 
how to fix that, but I'm not sure that it's worth the trouble since I 
also did some benchmarking and it appears that the benefit of special 
casing is minimal.

I looked at six cases: small (len-1), medium (len-1e4) and large 
(len-1e6) arrays with error checking on and error checking off. For 
medium and large arrays, I could discern no difference at all. For small 
arrays, there may be some difference, but it appears to be less than 5%. 
I'm not sure it's worth working through a bunch of finicky thread stuff 
to get just 5% back. If these benchmark numbers hold up I'd be inclined 
to rip out the use_default support since it's complicated enough that I 
know we'll end up chasing a few evil thread related bugs down through it.

I'll include the benchmarking code below. If people could (a) look it 
over and confirm that I'm not doing something bogus and (b) try it on 
some different platforms and see if they see a more signifigant 
difference, I'd appreciate it.

I'm also curious about the seterr interface. It returns 
ufunc_values_obj. I'm wasn't sure how one is supposed to pass that back 
in to seterr,  so I modified seterr to instead return a dictionary. I 
also modified it so that the seterr function itself has no defaults (or 
rather they're all None). Instead, any unspecified values are taken from 
the current error state. Thus seterr(divide="warn") changes only the 
divide state, leaving the other entries alone.


Regards,

-tim


if True:
    from timeit import Timer

    setup = """
import numpy
numpy.seterr(divide="%s")
a = numpy.zeros([%s], dtype=float)
"""
    for size in [1, 10000, 1000000]:
        for i in range(3):
            for state in ['ignore', 'warn']:
                reps = min(100000000 / size, 100000)
                timer = Timer("a * a", setup % (state, size))
                print "%s|%s =>" % (state, size), timer.timeit(reps)
            print
        print





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