Merged revisions 79583,79588-79589 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/trunk

........
  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.
........

1 files changed, 49 insertions, 18 deletions

diff --git a/Lib/decimal.py b/Lib/decimal.py
index ab38ed4..727aee2 100644
--- a/Lib/decimal.py
+++ b/Lib/decimal.py
@@ -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