Fix update method with legacy title* properties (plotly#1410)

Author: jonmmease

plotly/basedatatypes.py

@@ -2619,7 +2619,19 @@ def _get_prop_validator(self, prop):
         -------
         BaseValidator
         """
-        return self._validators[prop]
+
+        # Handle remapping
+        # ----------------
+        if prop in self._mapped_properties:
+            prop_path = self._mapped_properties[prop]
+            plotly_obj = self[prop_path[:-1]]
+            prop = prop_path[-1]
+        else:
+            plotly_obj = self
+
+        # Return validator
+        # ----------------
+        return plotly_obj._validators[prop]
 
     @property
     def parent(self):

plotly/tests/test_core/test_graph_objs/test_graph_objs.py

@@ -59,6 +59,14 @@ def test_title_as_string_layout(self):
             self.assertEqual(obj.to_plotly_json(),
                              {'title': {'text': 'A title 2'}})
 
+            # Update titlefont
+            obj.update(titlefont={'size': 23})
+            self.assertEqual(obj.title.font.size, 23)
+            self.assertEqual(obj.to_plotly_json(),
+                             {'title':
+                                  {'text': 'A title 2',
+                                   'font': {'size': 23}}})
+
         # Pie
         obj = go.Pie()
         obj.title = 'A title'
@@ -67,6 +75,22 @@ def test_title_as_string_layout(self):
                          {'title': {'text': 'A title'},
                           'type': 'pie'})
 
+        # And update
+        obj.update(title='A title 2')
+        self.assertEqual(obj.title.text, 'A title 2')
+        self.assertEqual(obj.to_plotly_json(),
+                         {'type': 'pie',
+                          'title': {'text': 'A title 2'}})
+
+        # Update titlefont
+        obj.update(titlefont={'size': 23})
+        self.assertEqual(obj.title.font.size, 23)
+        self.assertEqual(obj.to_plotly_json(),
+                         {'type': 'pie',
+                          'title':
+                              {'text': 'A title 2',
+                               'font': {'size': 23}}})
+
     def test_legacy_title_props_remapped(self):
 
         # plain Layout