From ae819ca6fd09e14a58842fc1e889f6737e53af0d Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
<31488909+miss-islington@users.noreply.github.com>
Date: Thu, 8 Sep 2022 04:03:53 -0700
Subject: [PATCH] [3.11] gh-68163: Correct conversion of Rational instances to
float (GH-25619) (#96556)
Co-authored-by: Mark Dickinson <dickinsm@gmail.com>
Co-authored-by: Sergey B Kirpichev <skirpichev@gmail.com>
---
Doc/library/numbers.rst | 9 ++++--
Lib/numbers.py | 2 +-
Lib/test/test_numeric_tower.py | 28 +++++++++++++++++++
...2-09-04-12-32-52.gh-issue-68163.h6TJCc.rst | 1 +
4 files changed, 36 insertions(+), 4 deletions(-)
create mode 100644 Misc/NEWS.d/next/Library/2022-09-04-12-32-52.gh-issue-68163.h6TJCc.rst
diff --git a/Doc/library/numbers.rst b/Doc/library/numbers.rst
index b12f82ed75a..b3dce151aee 100644
--- a/Doc/library/numbers.rst
+++ b/Doc/library/numbers.rst
@@ -58,11 +58,14 @@ The numeric tower
.. class:: Rational
- Subtypes :class:`Real` and adds
- :attr:`~Rational.numerator` and :attr:`~Rational.denominator` properties, which
- should be in lowest terms. With these, it provides a default for
+ Subtypes :class:`Real` and adds :attr:`~Rational.numerator` and
+ :attr:`~Rational.denominator` properties. It also provides a default for
:func:`float`.
+ The :attr:`~Rational.numerator` and :attr:`~Rational.denominator` values
+ should be instances of :class:`Integral` and should be in lowest terms with
+ :attr:`~Rational.denominator` positive.
+
.. attribute:: numerator
Abstract.
diff --git a/Lib/numbers.py b/Lib/numbers.py
index 5b98e642083..0985dd85f60 100644
--- a/Lib/numbers.py
+++ b/Lib/numbers.py
@@ -288,7 +288,7 @@ def __float__(self):
so that ratios of huge integers convert without overflowing.
"""
- return self.numerator / self.denominator
+ return int(self.numerator) / int(self.denominator)
class Integral(Rational):
diff --git a/Lib/test/test_numeric_tower.py b/Lib/test/test_numeric_tower.py
index c54dedb8b79..9cd85e13634 100644
--- a/Lib/test/test_numeric_tower.py
+++ b/Lib/test/test_numeric_tower.py
@@ -14,6 +14,27 @@
_PyHASH_MODULUS = sys.hash_info.modulus
_PyHASH_INF = sys.hash_info.inf
+
+class DummyIntegral(int):
+ """Dummy Integral class to test conversion of the Rational to float."""
+
+ def __mul__(self, other):
+ return DummyIntegral(super().__mul__(other))
+ __rmul__ = __mul__
+
+ def __truediv__(self, other):
+ return NotImplemented
+ __rtruediv__ = __truediv__
+
+ @property
+ def numerator(self):
+ return DummyIntegral(self)
+
+ @property
+ def denominator(self):
+ return DummyIntegral(1)
+
+
class HashTest(unittest.TestCase):
def check_equal_hash(self, x, y):
# check both that x and y are equal and that their hashes are equal
@@ -121,6 +142,13 @@ def test_fractions(self):
self.assertEqual(hash(F(7*_PyHASH_MODULUS, 1)), 0)
self.assertEqual(hash(F(-_PyHASH_MODULUS, 1)), 0)
+ # The numbers ABC doesn't enforce that the "true" division
+ # of integers produces a float. This tests that the
+ # Rational.__float__() method has required type conversions.
+ x = F(DummyIntegral(1), DummyIntegral(2), _normalize=False)
+ self.assertRaises(TypeError, lambda: x.numerator/x.denominator)
+ self.assertEqual(float(x), 0.5)
+
def test_hash_normalization(self):
# Test for a bug encountered while changing long_hash.
#
diff --git a/Misc/NEWS.d/next/Library/2022-09-04-12-32-52.gh-issue-68163.h6TJCc.rst b/Misc/NEWS.d/next/Library/2022-09-04-12-32-52.gh-issue-68163.h6TJCc.rst
new file mode 100644
index 00000000000..756f6c9eb9e
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-09-04-12-32-52.gh-issue-68163.h6TJCc.rst
@@ -0,0 +1 @@
+Correct conversion of :class:`numbers.Rational`'s to :class:`float`.
--
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