Add tests, update news entry

Author: ashkop

Lib/test/test_descr.py

@@ -3897,14 +3897,24 @@ def test_ipow_returns_not_implemented(self):
         class A:
             def __ipow__(self, other):
                 return NotImplemented
-        class B:
+        
+        class B(A):
             def __rpow__(self, other):
                 return 1
+
+        class C(A):
+            def __pow__(self, other):
+                return 2
         a = A()
         b = B()
+        c = C()
+
         a **= b
         self.assertEqual(a, 1)
 
+        c **= b
+        self.assertEqual(c, 2)
+
     def test_no_ipow(self):
         class B:
             def __rpow__(self, other):
@@ -3915,6 +3925,16 @@ def __rpow__(self, other):
         a **= b
         self.assertEqual(a, 1)
 
+    def test_ipow_exception_text(self):
+        x = None
+        with self.assertRaises(TypeError) as cm:
+            x **= 2
+        self.assertIn('unsupported operand type(s) for **=', str(cm.exception))
+
+        with self.assertRaises(TypeError) as cm:
+            y = x ** 2
+        self.assertIn('unsupported operand type(s) for **', str(cm.exception))
+
     def test_mutable_bases(self):
         # Testing mutable bases...
 

Misc/NEWS.d/next/Core and Builtins/2019-09-28-12-23-23.bpo-38302.hsCNgX.rst

@@ -1 +1 @@
-If :func:`operator.__ipow__` returns :const:`NotImplemented` :func:`operator.__rpow__` will be called now as expected.
+If :func:`object.__ipow__` returns :const:`NotImplemented`, the operator will correctly fall back to :func:`object.__pow__` and :func:`object.__rpow__` as expected.