Speed quirk: redundant line gives six-fold speedup
jack at performancedrivers.com
Thu Aug 25 20:29:36 CEST 2005
On Thu, Aug 25, 2005 at 09:23:09PM +0300, Stelios Xanthakis wrote:
> The explanation is this: hash
> and comparison of objects depends on the state of the memory
> allocator. A sample case is this:
> class A: pass
> dummy0=47 # comment this to get a different result for min
> print min (a, b)
> the result of 'min' is not only non-deterministic but also depends
> on whether other things have been allocated before. The same
> thing can happen for 'dictionary.keys()' if the keys are objects
> and 'iterate-over-set' when the set contains objects.
> In the sudoku solver, there is a min (number, object) which is
> probably what's affected by the extistance of the dummy variable.
> Now, in sudoku puzzles some times the algorithm has to suppose
Doh, I feel silly. Without an 'import random' in the program I
assumed it was deterministic. I would have also expected the
comparison to be a TypeError, and it sometimes is.
>>> mynum = 7
>>> myob = object()
>>> cmp(mynum, myob)
Traceback (most recent call last):
File "<stdin>", line 1, in ?
TypeError: int.__cmp__(x,y) requires y to be a 'int', not a 'object'
Thanks for the explanation,
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