set instantiate to True when constant is True (#771)

param/parameterized.py

@@ -1240,8 +1240,10 @@ def _set_instantiate(self,instantiate):
         # having this code avoids needless instantiation.
         if self.readonly:
             self.instantiate = False
+        elif self.constant is True:
+            self.instantiate = True
         elif instantiate is not Undefined:
-            self.instantiate = instantiate or self.constant # pylint: disable-msg=W0201
+            self.instantiate = instantiate
         else:
             # Default value
             self.instantiate = self._slot_defaults['instantiate']

tests/testparameterizedobject.py

@@ -274,6 +274,52 @@ def test_constant_parameter(self):
         testpo = TestPO()
         self.assertEqual(testpo.const,9)
 
+    def test_parameter_constant_instantiate(self):
+        # instantiate is automatically set to True when constant=True
+        assert TestPO.param.const.instantiate is True
+
+        class C(param.Parameterized):
+            # instantiate takes precedence when True
+            a = param.Parameter(instantiate=True, constant=False)
+            b = param.Parameter(instantiate=False, constant=False)
+            c = param.Parameter(instantiate=False, constant=True)
+            d = param.Parameter(constant=True)
+            e = param.Parameter(constant=False)
+            f = param.Parameter()
+
+        assert C.param.a.constant is False
+        assert C.param.a.instantiate is True
+        assert C.param.b.constant is False
+        assert C.param.b.instantiate is False
+        assert C.param.c.constant is True
+        assert C.param.c.instantiate is True
+        assert C.param.d.constant is True
+        assert C.param.d.instantiate is True
+        assert C.param.e.constant is False
+        assert C.param.e.instantiate is False
+        assert C.param.f.constant is False
+        assert C.param.f.instantiate is False
+
+    def test_parameter_constant_instantiate_subclass(self):
+
+        obj = object()
+
+        class A(param.Parameterized):
+            x = param.Parameter(obj)
+
+        class B(param.Parameterized):
+            x = param.Parameter(constant=True)
+
+        assert A.param.x.constant is False
+        assert A.param.x.instantiate is False
+        assert B.param.x.constant is True
+        assert B.param.x.instantiate is True
+
+        a = A()
+        b = B()
+        assert a.x is obj
+        assert b.x is not obj
+
     def test_readonly_parameter(self):
         """Test that you can't set a read-only parameter on construction or as an attribute."""
         testpo = TestPO()