Manual forward port of 64962 - use PyObject_HashNotImplemented as a tp_hash level indicator that the default hash implementation has not been inherited

Lib/decimal.py

@@ -3783,10 +3783,8 @@ class Context(object):
         for flag in flags:
             self._ignored_flags.remove(flag)
 
-    def __hash__(self):
-        """A Context cannot be hashed."""
-        # We inherit object.__hash__, so we must deny this explicitly
-        raise TypeError("Cannot hash a Context.")
+    # We inherit object.__hash__, so we must deny this explicitly
+    __hash__ = None
 
     def Etiny(self):
         """Returns Etiny (= Emin - prec + 1)"""

Lib/test/seq_tests.py

@@ -212,8 +212,7 @@ class CommonTest(unittest.TestCase):
             # So instances of AllEq must be found in all non-empty sequences.
             def __eq__(self, other):
                 return True
-            def __hash__(self):
-                raise NotImplemented
+            __hash__ = None # Can't meet hash invariant requirements
         self.assert_(AllEq() not in self.type2test([]))
         self.assert_(AllEq() in self.type2test([1]))
 

Lib/test/test_descr.py

@@ -3070,12 +3070,20 @@ order (MRO) for bases """
         self.assertEqual(hash(d), 144)
         D.__hash__ = lambda self: 100
         self.assertEqual(hash(d), 100)
+        D.__hash__ = None
+        self.assertRaises(TypeError, hash, d)
         del D.__hash__
         self.assertEqual(hash(d), 144)
+        B.__hash__ = None
+        self.assertRaises(TypeError, hash, d)
         del B.__hash__
         self.assertEqual(hash(d), 314)
+        C.__hash__ = None
+        self.assertRaises(TypeError, hash, d)
         del C.__hash__
         self.assertEqual(hash(d), 42)
+        A.__hash__ = None
+        self.assertRaises(TypeError, hash, d)
         del A.__hash__
         self.assertEqual(hash(d), orig_hash)
         d.foo = 42

Lib/test/test_hash.py

@@ -1,9 +1,11 @@
 # test the invariant that
 #   iff a==b then hash(a)==hash(b)
 #
+# Also test that hash implementations are inherited as expected
 
 import unittest
 from test import support
+from collections import Hashable
 
 
 class HashEqualityTestCase(unittest.TestCase):
@@ -37,8 +39,74 @@ class HashEqualityTestCase(unittest.TestCase):
         self.same_hash(float(0.5), complex(0.5, 0.0))
 
 
+_default_hash = object.__hash__
+class DefaultHash(object): pass
+
+_FIXED_HASH_VALUE = 42
+class FixedHash(object):
+    def __hash__(self):
+        return _FIXED_HASH_VALUE
+
+class OnlyEquality(object):
+    def __eq__(self, other):
+        return self is other
+
+class OnlyInequality(object):
+    def __ne__(self, other):
+        return self is not other
+
+class OnlyCmp(object):
+    def __cmp__(self, other):
+        return cmp(id(self), id(other))
+
+class InheritedHashWithEquality(FixedHash, OnlyEquality): pass
+class InheritedHashWithInequality(FixedHash, OnlyInequality): pass
+class InheritedHashWithCmp(FixedHash, OnlyCmp): pass
+
+class NoHash(object):
+    __hash__ = None
+
+class HashInheritanceTestCase(unittest.TestCase):
+    default_expected = [object(),
+                        DefaultHash(),
+                        OnlyInequality(),
+                       ]
+    fixed_expected = [FixedHash(),
+                      InheritedHashWithEquality(),
+                      InheritedHashWithInequality(),
+                      InheritedHashWithCmp(),
+                      ]
+    error_expected = [NoHash(),
+                      OnlyEquality(),
+                      OnlyCmp(),
+                      ]
+
+    def test_default_hash(self):
+        for obj in self.default_expected:
+            self.assertEqual(hash(obj), _default_hash(obj))
+
+    def test_fixed_hash(self):
+        for obj in self.fixed_expected:
+            self.assertEqual(hash(obj), _FIXED_HASH_VALUE)
+
+    def test_error_hash(self):
+        for obj in self.error_expected:
+            self.assertRaises(TypeError, hash, obj)
+
+    def test_hashable(self):
+        objects = (self.default_expected +
+                   self.fixed_expected)
+        for obj in objects:
+            self.assert_(isinstance(obj, Hashable), repr(obj))
+
+    def test_not_hashable(self):
+        for obj in self.error_expected:
+            self.assertFalse(isinstance(obj, Hashable), repr(obj))
+
+
 def test_main():
-    support.run_unittest(HashEqualityTestCase)
+    support.run_unittest(HashEqualityTestCase,
+                         HashInheritanceTestCase)
 
 
 if __name__ == "__main__":

Lib/test/test_richcmp.py

@@ -48,8 +48,7 @@ class Vector:
     def __setitem__(self, i, v):
         self.data[i] = v
 
-    def __hash__(self):
-        raise TypeError("Vectors cannot be hashed")
+    __hash__ = None # Vectors cannot be hashed
 
     def __bool__(self):
         raise TypeError("Vectors cannot be used in Boolean contexts")
@@ -85,35 +84,6 @@ class Vector:
             raise ValueError("Cannot compare vectors of different length")
         return other
 
-
-class SimpleOrder(object):
-    """
-    A simple class that defines order but not full comparison.
-    """
-
-    def __init__(self, value):
-        self.value = value
-
-    def __lt__(self, other):
-        if not isinstance(other, SimpleOrder):
-            return True
-        return self.value < other.value
-
-    def __gt__(self, other):
-        if not isinstance(other, SimpleOrder):
-            return False
-        return self.value > other.value
-
-
-class DumbEqualityWithoutHash(object):
-    """
-    A class that define __eq__, but no __hash__: it shouldn't be hashable.
-    """
-
-    def __eq__(self, other):
-        return False
-
-
 opmap = {
     "lt": (lambda a,b: a< b, operator.lt, operator.__lt__),
     "le": (lambda a,b: a<=b, operator.le, operator.__le__),
@@ -360,38 +330,8 @@ class ListTest(unittest.TestCase):
             self.assertIs(op(x, y), True)
 
 
-class HashableTest(unittest.TestCase):
-    """
-    Test hashability of classes with rich operators defined.
-    """
-
-    def test_simpleOrderHashable(self):
-        """
-        A class that only defines __gt__ and/or __lt__ should be hashable.
-        """
-        a = SimpleOrder(1)
-        b = SimpleOrder(2)
-        self.assert_(a < b)
-        self.assert_(b > a)
-        self.assert_(a.__hash__ is not None)
-
-    def test_notHashableException(self):
-        """
-        If a class is not hashable, it should raise a TypeError with an
-        understandable message.
-        """
-        a = DumbEqualityWithoutHash()
-        try:
-            hash(a)
-        except TypeError as e:
-            self.assertEquals(str(e),
-                              "unhashable type: 'DumbEqualityWithoutHash'")
-        else:
-            raise support.TestFailed("Should not be here")
-
-
 def test_main():
-    support.run_unittest(VectorTest, NumberTest, MiscTest, DictTest, ListTest, HashableTest)
+    support.run_unittest(VectorTest, NumberTest, MiscTest, DictTest, ListTest)
 
 if __name__ == "__main__":
     test_main()