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Merged revisions 79583,79588-79589 via svnmerge from 

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........
  r79583 | mark.dickinson | 2010-04-02 09:53:22 +0100 (Fri, 02 Apr 2010) | 7 lines

  Issue #2531: Make float-to-decimal comparisons return correct results.

  Float to decimal comparison operations now return a result based on
  the numeric values of the operands.  Decimal.__hash__ has also been
  fixed so that Decimal and float values that compare equal have equal
  hash value.
........
  r79588 | mark.dickinson | 2010-04-02 11:17:07 +0100 (Fri, 02 Apr 2010) | 2 lines

  Issue #7279:  Make comparisons involving a Decimal sNaN signal InvalidOperation.
........
  r79589 | mark.dickinson | 2010-04-02 11:35:12 +0100 (Fri, 02 Apr 2010) | 6 lines

  Issue #7279:  Make Decimal('nan') hashable.  Decimal('snan') remains unhashable.

  Also rewrite the Decimal __hash__ method so that it doesn't rely on
  float('inf') being valid: float('inf') could raise an exception on
  platforms not using IEEE 754 arithmetic.
........
This commit is contained in:
Mark Dickinson 2010-04-03 11:08:14 +00:00
parent 5fc16b469e
commit ac256ab284
4 changed files with 155 additions and 27 deletions
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18
Doc/library/decimal.rst
View File

@ -358,6 +358,24 @@ Decimal objects
compared, sorted, and coerced to another type (such as :class:`float` or
:class:`int`).
Decimal objects cannot generally be combined with floats in
arithmetic operations: an attempt to add a :class:`Decimal` to a
:class:`float`, for example, will raise a :exc:`TypeError`.
There's one exception to this rule: it's possible to use Python's
comparison operators to compare a :class:`float` instance ``x``
with a :class:`Decimal` instance ``y``. Without this exception,
comparisons between :class:`Decimal` and :class:`float` instances
would follow the general rules for comparing objects of different
types described in the :ref:`expressions` section of the reference
manual, leading to confusing results.
.. versionchanged:: 2.7
A comparison between a :class:`float` instance ``x`` and a
:class:`Decimal` instance ``y`` now returns a result based on
the values of ``x`` and ``y``. In earlier versions ``x < y``
returned the same (arbitrary) result for any :class:`Decimal`
instance ``x`` and any :class:`float` instance ``y``.
In addition to the standard numeric properties, decimal floating point
objects also have a number of specialized methods:

67
Lib/decimal.py
View File

@ -849,8 +849,11 @@ class Decimal(object):
# subject of what should happen for a comparison involving a NaN.
# We take the following approach:
#
# == comparisons involving a NaN always return False
# != comparisons involving a NaN always return True
# == comparisons involving a quiet NaN always return False
# != comparisons involving a quiet NaN always return True
# == or != comparisons involving a signaling NaN signal
# InvalidOperation, and return False or True as above if the
# InvalidOperation is not trapped.
# <, >, <= and >= comparisons involving a (quiet or signaling)
# NaN signal InvalidOperation, and return False if the
# InvalidOperation is not trapped.
@ -858,25 +861,25 @@ class Decimal(object):
# This behavior is designed to conform as closely as possible to
# that specified by IEEE 754.
def __eq__(self, other):
other = _convert_other(other)
def __eq__(self, other, context=None):
other = _convert_other(other, allow_float=True)
if other is NotImplemented:
return other
if self.is_nan() or other.is_nan():
if self._check_nans(other, context):
return False
return self._cmp(other) == 0
def __ne__(self, other):
other = _convert_other(other)
def __ne__(self, other, context=None):
other = _convert_other(other, allow_float=True)
if other is NotImplemented:
return other
if self.is_nan() or other.is_nan():
if self._check_nans(other, context):
return True
return self._cmp(other) != 0
def __lt__(self, other, context=None):
other = _convert_other(other)
other = _convert_other(other, allow_float=True)
if other is NotImplemented:
return other
ans = self._compare_check_nans(other, context)
@ -885,7 +888,7 @@ class Decimal(object):
return self._cmp(other) < 0
def __le__(self, other, context=None):
other = _convert_other(other)
other = _convert_other(other, allow_float=True)
if other is NotImplemented:
return other
ans = self._compare_check_nans(other, context)
@ -894,7 +897,7 @@ class Decimal(object):
return self._cmp(other) <= 0
def __gt__(self, other, context=None):
other = _convert_other(other)
other = _convert_other(other, allow_float=True)
if other is NotImplemented:
return other
ans = self._compare_check_nans(other, context)
@ -903,7 +906,7 @@ class Decimal(object):
return self._cmp(other) > 0
def __ge__(self, other, context=None):
other = _convert_other(other)
other = _convert_other(other, allow_float=True)
if other is NotImplemented:
return other
ans = self._compare_check_nans(other, context)
@ -937,12 +940,34 @@ class Decimal(object):
# The hash of a nonspecial noninteger Decimal must depend only
# on the value of that Decimal, and not on its representation.
# For example: hash(Decimal('100E-1')) == hash(Decimal('10')).
# Equality comparisons involving signaling nans can raise an
# exception; since equality checks are implicitly and
# unpredictably used when checking set and dict membership, we
# prevent signaling nans from being used as set elements or
# dict keys by making __hash__ raise an exception.
if self._is_special:
if self._isnan():
raise TypeError('Cannot hash a NaN value.')
return hash(str(self))
if not self:
return 0
if self.is_snan():
raise TypeError('Cannot hash a signaling NaN value.')
elif self.is_nan():
# 0 to match hash(float('nan'))
return 0
else:
# values chosen to match hash(float('inf')) and
# hash(float('-inf')).
if self._sign:
return -271828
else:
return 314159
# In Python 2.7, we're allowing comparisons (but not
# arithmetic operations) between floats and Decimals; so if
# a Decimal instance is exactly representable as a float then
# its hash should match that of the float.
self_as_float = float(self)
if Decimal.from_float(self_as_float) == self:
return hash(self_as_float)
if self._isinteger():
op = _WorkRep(self.to_integral_value())
# to make computation feasible for Decimals with large
@ -5780,15 +5805,21 @@ def _log10_lb(c, correction = {
##### Helper Functions ####################################################
def _convert_other(other, raiseit=False):
def _convert_other(other, raiseit=False, allow_float=False):
"""Convert other to Decimal.
Verifies that it's ok to use in an implicit construction.
If allow_float is true, allow conversion from float; this
is used in the comparison methods (__eq__ and friends).
"""
if isinstance(other, Decimal):
return other
if isinstance(other, int):
return Decimal(other)
if allow_float and isinstance(other, float):
return Decimal.from_float(other)
if raiseit:
raise TypeError("Unable to convert %s to Decimal" % other)
return NotImplemented

87
Lib/test/test_decimal.py
View File

@ -26,6 +26,7 @@ with the corresponding argument.
import math
import os, sys
import operator
import pickle, copy
import unittest
from decimal import *
@ -1096,18 +1097,56 @@ class DecimalArithmeticOperatorsTest(unittest.TestCase):
self.assertEqual(abs(Decimal(45)), abs(Decimal(-45))) # abs
def test_nan_comparisons(self):
# comparisons involving signaling nans signal InvalidOperation
# order comparisons (<, <=, >, >=) involving only quiet nans
# also signal InvalidOperation
# equality comparisons (==, !=) involving only quiet nans
# don't signal, but return False or True respectively.
n = Decimal('NaN')
s = Decimal('sNaN')
i = Decimal('Inf')
f = Decimal('2')
for x, y in [(n, n), (n, i), (i, n), (n, f), (f, n),
(s, n), (n, s), (s, i), (i, s), (s, f), (f, s), (s, s)]:
self.assertTrue(x != y)
self.assertTrue(not (x == y))
self.assertTrue(not (x < y))
self.assertTrue(not (x <= y))
self.assertTrue(not (x > y))
self.assertTrue(not (x >= y))
qnan_pairs = (n, n), (n, i), (i, n), (n, f), (f, n)
snan_pairs = (s, n), (n, s), (s, i), (i, s), (s, f), (f, s), (s, s)
order_ops = operator.lt, operator.le, operator.gt, operator.ge
equality_ops = operator.eq, operator.ne
# results when InvalidOperation is not trapped
for x, y in qnan_pairs + snan_pairs:
for op in order_ops + equality_ops:
got = op(x, y)
expected = True if op is operator.ne else False
self.assertIs(expected, got,
"expected {0!r} for operator.{1}({2!r}, {3!r}); "
"got {4!r}".format(
expected, op.__name__, x, y, got))
# repeat the above, but this time trap the InvalidOperation
with localcontext() as ctx:
ctx.traps[InvalidOperation] = 1
for x, y in qnan_pairs:
for op in equality_ops:
got = op(x, y)
expected = True if op is operator.ne else False
self.assertIs(expected, got,
"expected {0!r} for "
"operator.{1}({2!r}, {3!r}); "
"got {4!r}".format(
expected, op.__name__, x, y, got))
for x, y in snan_pairs:
for op in equality_ops:
self.assertRaises(InvalidOperation, operator.eq, x, y)
self.assertRaises(InvalidOperation, operator.ne, x, y)
for x, y in qnan_pairs + snan_pairs:
for op in order_ops:
self.assertRaises(InvalidOperation, op, x, y)
def test_copy_sign(self):
d = Decimal(1).copy_sign(Decimal(-2))
@ -1213,6 +1252,23 @@ class DecimalUsabilityTest(unittest.TestCase):
a.sort()
self.assertEqual(a, b)
def test_decimal_float_comparison(self):
da = Decimal('0.25')
db = Decimal('3.0')
self.assert_(da < 3.0)
self.assert_(da <= 3.0)
self.assert_(db > 0.25)
self.assert_(db >= 0.25)
self.assert_(da != 1.5)
self.assert_(da == 0.25)
self.assert_(3.0 > da)
self.assert_(3.0 >= da)
self.assert_(0.25 < db)
self.assert_(0.25 <= db)
self.assert_(0.25 != db)
self.assert_(3.0 == db)
self.assert_(0.1 != Decimal('0.1'))
def test_copy_and_deepcopy_methods(self):
d = Decimal('43.24')
c = copy.copy(d)
@ -1223,6 +1279,10 @@ class DecimalUsabilityTest(unittest.TestCase):
def test_hash_method(self):
#just that it's hashable
hash(Decimal(23))
hash(Decimal('Infinity'))
hash(Decimal('-Infinity'))
hash(Decimal('nan123'))
hash(Decimal('-NaN'))
test_values = [Decimal(sign*(2**m + n))
for m in [0, 14, 15, 16, 17, 30, 31,
@ -1257,10 +1317,19 @@ class DecimalUsabilityTest(unittest.TestCase):
#the same hash that to an int
self.assertEqual(hash(Decimal(23)), hash(23))
self.assertRaises(TypeError, hash, Decimal('NaN'))
self.assertRaises(TypeError, hash, Decimal('sNaN'))
self.assertTrue(hash(Decimal('Inf')))
self.assertTrue(hash(Decimal('-Inf')))
# check that the hashes of a Decimal float match when they
# represent exactly the same values
test_strings = ['inf', '-Inf', '0.0', '-.0e1',
'34.0', '2.5', '112390.625', '-0.515625']
for s in test_strings:
f = float(s)
d = Decimal(s)
self.assertEqual(hash(f), hash(d))
# check that the value of the hash doesn't depend on the
# current context (issue #1757)
c = getcontext()

10
Misc/NEWS
View File

@ -301,6 +301,16 @@ C-API
Library
-------
- Issue #7279: Comparisons involving a Decimal signaling NaN now
signal InvalidOperation instead of returning False. (Comparisons
involving a quiet NaN are unchanged.) Also, Decimal quiet NaNs
are now hashable; Decimal signaling NaNs remain unhashable.
- Issue #2531: Comparison operations between floats and Decimal
instances now return a result based on the numeric values of the
operands; previously they returned an arbitrary result based on
the relative ordering of id(float) and id(Decimal).
- Added a subtract() method to collections.Counter().
- Issue #8233: When run as a script, py_compile.py optionally takes a single