[issue25177] OverflowError in statistics.mean when summing large floats
Mark Dickinson
report at bugs.python.org
Tue Oct 20 02:44:40 EDT 2015
Mark Dickinson added the comment:
> I strongly suspect that moving from float to Fraction-based ratios is going to kill performance in the common case
The existing code already converts each of the input items to Fraction; the only difference is that the old code converts the sum of those Fractions to float (or whatever the target type is) *before* dividing by the count, while the new code performs the sum/count division in Fraction-land, and only *then* converts to float. That is, it's the difference between "float(exact_sum) / count" and "float(exact_sum / count)".
IOW, the performance is already dead. Or rather, it's just resting: IIUC, the module design prioritises correctness over speed. I'm sure Steven would be open to suggestions for faster algorithms that maintain the current accuracy.
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<http://bugs.python.org/issue25177>
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