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bpo-20499: Rounding error in statistics.pvariance #28230

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Merged
rhettinger merged 12 commits into from
Sep 9, 2021
Merged

bpo-20499: Rounding error in statistics.pvariance #28230

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0a1d350
Incorrect first draft
rhettinger Sep 8, 2021
d8714cc
Exact ss
rhettinger Sep 8, 2021
2108d4d
Add test
rhettinger Sep 8, 2021
da6c6cb
Add blurb
rhettinger Sep 8, 2021
69387c6
Remove superfluous comment
rhettinger Sep 8, 2021
39973fd
Add another test
rhettinger Sep 8, 2021
829d5ec
Improve clairity
rhettinger Sep 8, 2021
cc78aaf
Beautify the order of terms
rhettinger Sep 8, 2021
c0b1560
Removed unused "start" argument from internal function
rhettinger Sep 8, 2021
c746482
Modernize and speed-up _exact_ratio() internal function
rhettinger Sep 8, 2021
e7c46fa
Remove unnecessary sort
rhettinger Sep 8, 2021
117ad6b
Add accuracy comments to stdev() and pstdev().
rhettinger Sep 8, 2021
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Modernize and speed-up _exact_ratio() internal function
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@rhettinger
rhettinger committed Sep 8, 2021
commit c74648287fa56bbe5755b23df600b0cb4f246951
26 changes: 9 additions & 17 deletions Lib/statistics.py
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Original file line number Diff line number Diff line change
Expand Up @@ -247,27 +247,19 @@ def _exact_ratio(x):
x is expected to be an int, Fraction, Decimal or float.
"""
try:
# Optimise the common case of floats. We expect that the most often
# used numeric type will be builtin floats, so try to make this as
# fast as possible.
if type(x) is float or type(x) is Decimal:
return x.as_integer_ratio()
try:
# x may be an int, Fraction, or Integral ABC.
return (x.numerator, x.denominator)
except AttributeError:
try:
# x may be a float or Decimal subclass.
return x.as_integer_ratio()
except AttributeError:
# Just give up?
pass
return x.as_integer_ratio()
except AttributeError:
pass
except (OverflowError, ValueError):
# float NAN or INF.
assert not _isfinite(x)
return (x, None)
msg = "can't convert type '{}' to numerator/denominator"
raise TypeError(msg.format(type(x).__name__))
try:
# x may be an Integral ABC.
return (x.numerator, x.denominator)
except AttributeError:
msg = f"can't convert type '{type(x).__name__}' to numerator/denominator"
raise TypeError(msg)


def _convert(value, T):
Expand Down