Reed <rea...@gmail.com> added the comment:
Thank you all for the comments! Either using (x-c)*(x-c), or removing the
assertion and changing the final line to `return (U, total)`, seem reasonable.
I slightly prefer the latter case, due to Mark's comments about x*x being
faster and simpler than x**2. But I am not an expert on this.
> I am inclined to have the stdev of float32 return a float32 is possible. What
> do you think?
Agreed.
> OTOH, (x-c)*(x-c) repeats the subtraction unnecessarily, but perhaps
> assignment expressions could rescue us?
Yeah, we should avoid repeating the subtraction. Another method of doing so is
to define a square function. For example:
def square(y):
return y*y
sum(square(x-c) for x in data)
> Would that also imply intermediate calculations being performed only with
> float32, or would intermediate calculations be performed with a more precise
> type?
Currently, statistics.py computes sums in infinite precision
(https://github.com/python/cpython/blob/422ed16fb846eec0b5b2a4eb3a978c9862615665/Lib/statistics.py#L123)
for any type. The multiplications (and exponents if we go that route) would
still be float32.
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue39218>
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