Issue #27539: Fix unnormalised Fraction.__pow__ result for negative exponent and base. Thanks Vedran Čačić.
diff --git a/Lib/fractions.py b/Lib/fractions.py
index 60b0728..9aabab3 100644
--- a/Lib/fractions.py
+++ b/Lib/fractions.py
@@ -484,10 +484,14 @@
return Fraction(a._numerator ** power,
a._denominator ** power,
_normalize=False)
- else:
+ elif a._numerator >= 0:
return Fraction(a._denominator ** -power,
a._numerator ** -power,
_normalize=False)
+ else:
+ return Fraction((-a._denominator) ** -power,
+ (-a._numerator) ** -power,
+ _normalize=False)
else:
# A fractional power will generally produce an
# irrational number.
diff --git a/Lib/test/test_fractions.py b/Lib/test/test_fractions.py
index 1699852..9df4a54 100644
--- a/Lib/test/test_fractions.py
+++ b/Lib/test/test_fractions.py
@@ -356,6 +356,19 @@
z = pow(F(-1), F(1, 2))
self.assertAlmostEqual(z.real, 0)
self.assertEqual(z.imag, 1)
+ # Regression test for #27539.
+ p = F(-1, 2) ** 0
+ self.assertEqual(p, F(1, 1))
+ self.assertEqual(p.numerator, 1)
+ self.assertEqual(p.denominator, 1)
+ p = F(-1, 2) ** -1
+ self.assertEqual(p, F(-2, 1))
+ self.assertEqual(p.numerator, -2)
+ self.assertEqual(p.denominator, 1)
+ p = F(-1, 2) ** -2
+ self.assertEqual(p, F(4, 1))
+ self.assertEqual(p.numerator, 4)
+ self.assertEqual(p.denominator, 1)
def testMixedArithmetic(self):
self.assertTypedEquals(F(11, 10), F(1, 10) + 1)
diff --git a/Misc/ACKS b/Misc/ACKS
index 51c8d10..1c9363a 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -217,6 +217,7 @@
Ralph Butler
Laurent De Buyst
Zach Byrne
+Vedran Čačić
Nicolas Cadou
Jp Calderone
Arnaud Calmettes
diff --git a/Misc/NEWS b/Misc/NEWS
index 54cae1d..7530624 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -46,6 +46,9 @@
Library
-------
+- Issue #27539: Fix unnormalised ``Fraction.__pow__`` result in the case
+ of negative exponent and negative base.
+
- Issue #21718: cursor.description is now available for queries using CTEs.
- Issue #2466: posixpath.ismount now correctly recognizes mount points which