Fix Decimal hash in Python 2.5 maintenance branch so that hash(x) == hash(int(x))

for any integral Decimal instance x.

Lib/decimal.py

@@ -800,13 +800,7 @@ def __hash__(self):
             return 0
         if self._isinteger():
             op = _WorkRep(self.to_integral_value())
-            # to make computation feasible for Decimals with large
-            # exponent, we use the fact that hash(n) == hash(m) for
-            # any two nonzero integers n and m such that (i) n and m
-            # have the same sign, and (ii) n is congruent to m modulo
-            # 2**64-1.  So we can replace hash((-1)**s*c*10**e) with
-            # hash((-1)**s*c*pow(10, e, 2**64-1).
-            return hash((-1)**op.sign*op.int*pow(10, op.exp, 2**64-1))
+            return hash((-1)**op.sign*op.int*10**op.exp)
         # The value of a nonzero nonspecial Decimal instance is
         # faithfully represented by the triple consisting of its sign,
         # its adjusted exponent, and its coefficient with trailing

Lib/test/test_decimal.py

@@ -961,6 +961,16 @@ def test_hash_method(self):
                 # a value for which hash(n) != hash(n % (2**64-1))
                 # in Python pre-2.6
                 Decimal(2**64 + 2**32 - 1),
+                # selection of values which fail with the Python 2.6
+                # version of Decimal.__hash__ and the Python 2.5
+                # version of long.__hash__.  Included here to prevent
+                # an accidental backport of the Decimal.__hash__ from
+                # Python 2.6 to Python 2.5.
+                Decimal("1.634E100"),
+                Decimal("90.697E100"),
+                Decimal("188.83E100"),
+                Decimal("1652.9E100"),
+                Decimal("56531E100"),
                 ])
 
         # check that hash(d) == hash(int(d)) for integral values