Issue #6431: Fix Fraction comparisons to return NotImplemented when

the Fraction type doesn't know how to handle the comparison without
loss of accuracy.  Also, make sure that comparisons between Fractions
and float infinities or nans do the right thing.

1 files changed, 126 insertions, 0 deletions

diff --git a/Lib/test/test_fractions.py b/Lib/test/test_fractions.py
index e32191452c..fd6588a1fe 100644
--- a/Lib/test/test_fractions.py
+++ b/Lib/test/test_fractions.py
@@ -3,6 +3,7 @@
 from decimal import Decimal
 from test.support import run_unittest
 import math
+import numbers
 import operator
 import fractions
 import unittest
@@ -11,6 +12,69 @@ from pickle import dumps, loads
 F = fractions.Fraction
 gcd = fractions.gcd
 
+class DummyFloat(object):
+    """Dummy float class for testing comparisons with Fractions"""
+
+    def __init__(self, value):
+        if not isinstance(value, float):
+            raise TypeError("DummyFloat can only be initialized from float")
+        self.value = value
+
+    def _richcmp(self, other, op):
+        if isinstance(other, numbers.Rational):
+            return op(F.from_float(self.value), other)
+        elif isinstance(other, DummyFloat):
+            return op(self.value, other.value)
+        else:
+            return NotImplemented
+
+    def __eq__(self, other): return self._richcmp(other, operator.eq)
+    def __le__(self, other): return self._richcmp(other, operator.le)
+    def __lt__(self, other): return self._richcmp(other, operator.lt)
+    def __ge__(self, other): return self._richcmp(other, operator.ge)
+    def __gt__(self, other): return self._richcmp(other, operator.gt)
+
+    # shouldn't be calling __float__ at all when doing comparisons
+    def __float__(self):
+        assert False, "__float__ should not be invoked for comparisons"
+
+    # same goes for subtraction
+    def __sub__(self, other):
+        assert False, "__sub__ should not be invoked for comparisons"
+    __rsub__ = __sub__
+
+
+class DummyRational(object):
+    """Test comparison of Fraction with a naive rational implementation."""
+
+    def __init__(self, num, den):
+        g = gcd(num, den)
+        self.num = num // g
+        self.den = den // g
+
+    def __eq__(self, other):
+        if isinstance(other, fractions.Fraction):
+            return (self.num == other._numerator and
+                    self.den == other._denominator)
+        else:
+            return NotImplemented
+
+    def __lt__(self, other):
+        return(self.num * other._denominator < self.den * other._numerator)
+
+    def __gt__(self, other):
+        return(self.num * other._denominator > self.den * other._numerator)
+
+    def __le__(self, other):
+        return(self.num * other._denominator <= self.den * other._numerator)
+
+    def __ge__(self, other):
+        return(self.num * other._denominator >= self.den * other._numerator)
+
+    # this class is for testing comparisons; conversion to float
+    # should never be used for a comparison, since it loses accuracy
+    def __float__(self):
+        assert False, "__float__ should not be invoked"
 
 class GcdTest(unittest.TestCase):
 
@@ -324,6 +388,50 @@ class FractionTest(unittest.TestCase):
         self.assertFalse(F(1, 2) != F(1, 2))
         self.assertTrue(F(1, 2) != F(1, 3))
 
+    def testComparisonsDummyRational(self):
+        self.assertTrue(F(1, 2) == DummyRational(1, 2))
+        self.assertTrue(DummyRational(1, 2) == F(1, 2))
+        self.assertFalse(F(1, 2) == DummyRational(3, 4))
+        self.assertFalse(DummyRational(3, 4) == F(1, 2))
+
+        self.assertTrue(F(1, 2) < DummyRational(3, 4))
+        self.assertFalse(F(1, 2) < DummyRational(1, 2))
+        self.assertFalse(F(1, 2) < DummyRational(1, 7))
+        self.assertFalse(F(1, 2) > DummyRational(3, 4))
+        self.assertFalse(F(1, 2) > DummyRational(1, 2))
+        self.assertTrue(F(1, 2) > DummyRational(1, 7))
+        self.assertTrue(F(1, 2) <= DummyRational(3, 4))
+        self.assertTrue(F(1, 2) <= DummyRational(1, 2))
+        self.assertFalse(F(1, 2) <= DummyRational(1, 7))
+        self.assertFalse(F(1, 2) >= DummyRational(3, 4))
+        self.assertTrue(F(1, 2) >= DummyRational(1, 2))
+        self.assertTrue(F(1, 2) >= DummyRational(1, 7))
+
+        self.assertTrue(DummyRational(1, 2) < F(3, 4))
+        self.assertFalse(DummyRational(1, 2) < F(1, 2))
+        self.assertFalse(DummyRational(1, 2) < F(1, 7))
+        self.assertFalse(DummyRational(1, 2) > F(3, 4))
+        self.assertFalse(DummyRational(1, 2) > F(1, 2))
+        self.assertTrue(DummyRational(1, 2) > F(1, 7))
+        self.assertTrue(DummyRational(1, 2) <= F(3, 4))
+        self.assertTrue(DummyRational(1, 2) <= F(1, 2))
+        self.assertFalse(DummyRational(1, 2) <= F(1, 7))
+        self.assertFalse(DummyRational(1, 2) >= F(3, 4))
+        self.assertTrue(DummyRational(1, 2) >= F(1, 2))
+        self.assertTrue(DummyRational(1, 2) >= F(1, 7))
+
+    def testComparisonsDummyFloat(self):
+        x = DummyFloat(1./3.)
+        y = F(1, 3)
+        self.assertTrue(x != y)
+        self.assertTrue(x < y or x > y)
+        self.assertFalse(x == y)
+        self.assertFalse(x <= y and x >= y)
+        self.assertTrue(y != x)
+        self.assertTrue(y < x or y > x)
+        self.assertFalse(y == x)
+        self.assertFalse(y <= x and y >= x)
+
     def testMixedLess(self):
         self.assertTrue(2 < F(5, 2))
         self.assertFalse(2 < F(4, 2))
@@ -335,6 +443,13 @@ class FractionTest(unittest.TestCase):
         self.assertTrue(0.4 < F(1, 2))
         self.assertFalse(0.5 < F(1, 2))
 
+        self.assertFalse(float('inf') < F(1, 2))
+        self.assertTrue(float('-inf') < F(0, 10))
+        self.assertFalse(float('nan') < F(-3, 7))
+        self.assertTrue(F(1, 2) < float('inf'))
+        self.assertFalse(F(17, 12) < float('-inf'))
+        self.assertFalse(F(144, -89) < float('nan'))
+
     def testMixedLessEqual(self):
         self.assertTrue(0.5 <= F(1, 2))
         self.assertFalse(0.6 <= F(1, 2))
@@ -345,6 +460,13 @@ class FractionTest(unittest.TestCase):
         self.assertTrue(F(4, 2) <= 2)
         self.assertFalse(F(5, 2) <= 2)
 
+        self.assertFalse(float('inf') <= F(1, 2))
+        self.assertTrue(float('-inf') <= F(0, 10))
+        self.assertFalse(float('nan') <= F(-3, 7))
+        self.assertTrue(F(1, 2) <= float('inf'))
+        self.assertFalse(F(17, 12) <= float('-inf'))
+        self.assertFalse(F(144, -89) <= float('nan'))
+
     def testBigFloatComparisons(self):
         # Because 10**23 can't be represented exactly as a float:
         self.assertFalse(F(10**23) == float(10**23))
@@ -369,6 +491,10 @@ class FractionTest(unittest.TestCase):
         self.assertFalse(2 == F(3, 2))
         self.assertTrue(F(4, 2) == 2)
         self.assertFalse(F(5, 2) == 2)
+        self.assertFalse(F(5, 2) == float('nan'))
+        self.assertFalse(float('nan') == F(3, 7))
+        self.assertFalse(F(5, 2) == float('inf'))
+        self.assertFalse(float('-inf') == F(2, 5))
 
     def testStringification(self):
         self.assertEquals("Fraction(7, 3)", repr(F(7, 3)))