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Merged revisions 74078 via svnmerge from 

svn+ssh://pythondev@www.python.org/python/branches/py3k

........
  r74078 | mark.dickinson | 2009-07-18 15:41:42 +0100 (Sat, 18 Jul 2009) | 5 lines

  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.
........
This commit is contained in:
Mark Dickinson 2009-07-18 14:43:10 +00:00
parent 680ac292ac
commit 8d15643a4b
3 changed files with 162 additions and 30 deletions
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62
Lib/fractions.py
View File

@ -501,54 +501,56 @@ class Fraction(numbers.Rational):
if isinstance(b, numbers.Complex) and b.imag == 0:
b = b.real
if isinstance(b, float):
return a == a.from_float(b)
if math.isnan(b) or math.isinf(b):
# comparisons with an infinity or nan should behave in
# the same way for any finite a, so treat a as zero.
return 0.0 == b
else:
return a == a.from_float(b)
else:
# XXX: If b.__eq__ is implemented like this method, it may
# give the wrong answer after float(a) changes a's
# value. Better ways of doing this are welcome.
return float(a) == b
# Since a doesn't know how to compare with b, let's give b
# a chance to compare itself with a.
return NotImplemented
def _subtractAndCompareToZero(a, b, op):
"""Helper function for comparison operators.
def _richcmp(self, other, op):
"""Helper for comparison operators, for internal use only.
Subtracts b from a, exactly if possible, and compares the
result with 0 using op, in such a way that the comparison
won't recurse. If the difference raises a TypeError, returns
NotImplemented instead.
Implement comparison between a Rational instance `self`, and
either another Rational instance or a float `other`. If
`other` is not a Rational instance or a float, return
NotImplemented. `op` should be one of the six standard
comparison operators.
"""
if isinstance(b, numbers.Complex) and b.imag == 0:
b = b.real
if isinstance(b, float):
b = a.from_float(b)
try:
# XXX: If b <: Real but not <: Rational, this is likely
# to fall back to a float. If the actual values differ by
# less than MIN_FLOAT, this could falsely call them equal,
# which would make <= inconsistent with ==. Better ways of
# doing this are welcome.
diff = a - b
except TypeError:
# convert other to a Rational instance where reasonable.
if isinstance(other, numbers.Rational):
return op(self._numerator * other.denominator,
self._denominator * other.numerator)
if isinstance(other, numbers.Complex) and other.imag == 0:
other = other.real
if isinstance(other, float):
if math.isnan(other) or math.isinf(other):
return op(0.0, other)
else:
return op(self, self.from_float(other))
else:
return NotImplemented
if isinstance(diff, numbers.Rational):
return op(diff.numerator, 0)
return op(diff, 0)
def __lt__(a, b):
"""a < b"""
return a._subtractAndCompareToZero(b, operator.lt)
return a._richcmp(b, operator.lt)
def __gt__(a, b):
"""a > b"""
return a._subtractAndCompareToZero(b, operator.gt)
return a._richcmp(b, operator.gt)
def __le__(a, b):
"""a <= b"""
return a._subtractAndCompareToZero(b, operator.le)
return a._richcmp(b, operator.le)
def __ge__(a, b):
"""a >= b"""
return a._subtractAndCompareToZero(b, operator.ge)
return a._richcmp(b, operator.ge)
def __bool__(a):
"""a != 0"""

126
Lib/test/test_fractions.py
View File

@ -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)))

4
Misc/NEWS
View File

@ -34,6 +34,10 @@ C-API
Library
-------
- Issue #6431: Make Fraction type return NotImplemented when it doesn't
know how to handle a comparison without loss of precision. Also add
correct handling of infinities and nans for comparisons with float.
- Issue #6415: Fixed warnings.warn sagfault on bad formatted string.
- Issue #6358: The exit status of a command started with os.popen() was