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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.
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  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.
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  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.
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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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67
Lib/decimal.py
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@ -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