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Remove support for nth root of negative numbers with odd powers.

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Although nth roots of negative numbers are real for odd n, the
statistics module doesn't make use of this. Remove support for
negative roots from the private _nth_root function, which
simplifies the test suite.
This commit is contained in:
Steven D'Aprano 2016-08-24 12:48:12 +10:00
parent e5803d9d2f
commit d6ea3011c5
2 changed files with 8 additions and 28 deletions
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7
Lib/statistics.py
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@ -335,10 +335,7 @@ class _nroot_NS:
"""Handle nth root of Reals, treated as a float."""
assert isinstance(n, int) and n > 1
if x < 0:
if n%2 == 0:
raise ValueError('domain error: even root of negative number')
else:
return -_nroot_NS.nroot(-x, n)
raise ValueError('domain error: root of negative number')
elif x == 0:
return math.copysign(0.0, x)
elif x > 0:
@ -433,6 +430,8 @@ class _nroot_NS:
else:
# Preserve the input NAN.
return x
if x < 0:
raise ValueError('domain error: root of negative number')
if x.is_infinite():
return x
# FIXME this hasn't had the extensive testing of the float