Fix default Object __eq__ and __ne__

- For objects which don’t override __eq__ and __ne__, they should
return True/False respectively when comparing an object against itself,
and otherwise NotImplemented instead of False.

python/common/org/python/types/Object.java

@@ -205,7 +205,11 @@ public org.python.Object __le__(org.python.Object other) {
         args = {"other"}
     )
     public org.python.Object __eq__(org.python.Object other) {
-        return new org.python.types.Bool(System.identityHashCode(this) == System.identityHashCode(other));
+        if (this == other) {
+            return new org.python.types.Bool(true);
+        } else {
+            return org.python.types.NotImplementedType.NOT_IMPLEMENTED;
+        }
     }
 
     @org.python.Method(

tests/structures/test_comparisons.py

@@ -204,6 +204,33 @@ def test_ne(self):
                 print('False')
             """)
 
+    def test_eq_empty_class(self):
+        self.assertCodeExecution("""
+            class A:
+                pass
+            x = A()
+            y = A()
+            # fallback to object identity
+            print(x == x)
+            print(x == y)
+            print(x.__eq__(x))
+            print(x.__eq__(y))
+            print(y.__eq__(x))
+            """)
+
+    def test_ne_empty_class(self):
+        self.assertCodeExecution("""
+            class A:
+                pass
+            x = A()
+            y = A()
+            print(x != x)
+            print(x != y)
+            print(x.__ne__(x))
+            print(x.__ne__(y))
+            print(y.__ne__(x))
+            """)
+
     # next few tests from cpython's Lib/test/test_compare.py @ v3.6.0
     def test_comparisons(self):
         self.assertCodeExecution("""