Fix for #1050. Can't create numbered subplots in update

Author: jonmmease

plotly/basedatatypes.py

@@ -2100,6 +2100,18 @@ def _perform_update(plotly_obj, update_obj):
             return
         elif isinstance(plotly_obj, BasePlotlyType):
 
+            # Handle initializing subplot ids
+            # -------------------------------
+            # This should be valid even if xaxis2 hasn't been initialized:
+            # >>> layout.update(xaxis2={'title': 'xaxis 2'})
+            if isinstance(plotly_obj, BaseLayoutType):
+                for key in update_obj:
+                    if key not in plotly_obj:
+                        match = fullmatch(plotly_obj._subplotid_prop_re, key)
+                        if match:
+                            # We need to create a subplotid object
+                            plotly_obj[key] = {}
+
             # Handle invalid properties
             # -------------------------
             invalid_props = [

plotly/tests/test_core/test_graph_objs/test_layout_subplots.py

@@ -153,3 +153,31 @@ def test_subplot_props_in_constructor(self):
         self.assertEqual(layout.geo4.bgcolor, 'blue')
         self.assertEqual(layout.ternary5.sum, 120)
         self.assertEqual(layout.scene6.dragmode, 'zoom')
+
+    def test_create_subplot_with_update(self):
+
+        self.layout.update(xaxis2=go.layout.XAxis(title='xaxis 2'),
+                           yaxis3=go.layout.YAxis(title='yaxis 3'),
+                           geo4=go.layout.Geo(bgcolor='blue'),
+                           ternary5=go.layout.Ternary(sum=120),
+                           scene6=go.layout.Scene(dragmode='zoom'))
+
+        self.assertEqual(self.layout.xaxis2.title, 'xaxis 2')
+        self.assertEqual(self.layout.yaxis3.title, 'yaxis 3')
+        self.assertEqual(self.layout.geo4.bgcolor, 'blue')
+        self.assertEqual(self.layout.ternary5.sum, 120)
+        self.assertEqual(self.layout.scene6.dragmode, 'zoom')
+
+    def test_create_subplot_with_update_dict(self):
+
+        self.layout.update({'xaxis2': {'title': 'xaxis 2'},
+                            'yaxis3': {'title': 'yaxis 3'},
+                            'geo4': {'bgcolor': 'blue'},
+                            'ternary5': {'sum': 120},
+                            'scene6': {'dragmode': 'zoom'}})
+
+        self.assertEqual(self.layout.xaxis2.title, 'xaxis 2')
+        self.assertEqual(self.layout.yaxis3.title, 'yaxis 3')
+        self.assertEqual(self.layout.geo4.bgcolor, 'blue')
+        self.assertEqual(self.layout.ternary5.sum, 120)
+        self.assertEqual(self.layout.scene6.dragmode, 'zoom')