On 22/04/2013 18:48, Skip Montanaro wrote:
>> But I was really wondering if there was a simple solution that worked
>> without people having to add libraries to their basic Python installations.
>
> I think installing numpy is approximately
>
> pip install numpy
>
> assuming you have write access to your site-packages directory. If
> not, install using --prefix and set PYTHONPATH accordingly.
>
> I forgot that Python also has an array module. With numpy available,
> mature, and well-supported, I imagine it doesn't get much love these
> days though. Still, I gave it a whirl:
>
> #######################################
> import random
> import array
> from timeit import Timer
>
> import numpy
>
> stuff = [random.random() < 0.5 for i in range(10**7)]
> sieve1 = numpy.array(stuff, dtype=bool)
> sieve2 = array.array('B', stuff)
>
> setup = """from __main__ import sieve1, sieve2
> from itertools import islice
> hi = 7*10**6
> """
>
> t1 = Timer("(True == sieve1[:hi]).sum()", setup)
> t2 = Timer("sieve2[:hi].count(True)", setup)
> # t3 = Timer("sum(islice(sieve, hi))", setup)
> # t4 = Timer("sum(x for x in islice(sieve, hi) if x)", setup)
> # t5 = Timer("sum(x for x in islice(sieve, hi) if x is True)", setup)
> # t6 = Timer("sum(1 for x in islice(sieve, hi) if x is True)", setup)
> # t7 = Timer("len(list(filter(None, islice(sieve, hi))))", setup)
>
> print(min(t1.repeat(number=10)))
> print(min(t2.repeat(number=10)))
> # for t in (t1, t2, t3, t4, t5, t6, t7):
> # print( min(t.repeat(number=10)) )
> #######################################
>
> Performance was not all that impressive:
>
> 0.340315103531
> 5.42102503777
>
> Still, you might fiddle around with it a bit. Perhaps unsigned ints
> instead of unsigned bytes will provide more efficient counting...
I spent a lot of time comparing python arrays and lists but found that
lists were always much faster in this application.
I do have numpy installed but I remember that when I did this (some time
ago) it was far from easy with Python 3.x running natively on Windows x64.
Brian
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