make _grid_ref and _grid_str attributes

Author: etpinard

plotly/graph_objs/graph_objs.py

@@ -922,7 +922,7 @@ def __init__(self, *args, **kwargs):
 
     def print_grid(self):
         try:
-            grid_str = self['_grid_str']
+            grid_str = self._grid_str
         except KeyError:
             raise Exception("Use tools.make_subplots "
                             "to create a subplot grid.")
@@ -931,7 +931,7 @@ def print_grid(self):
 
     def append_trace(self, trace, row, col):
         try:
-            grid_ref = self['_grid_ref']
+            grid_ref = self._grid_ref
         except KeyError:
             raise Exception("In order to use Figure.append_trace, "
                             "you must first use tools.make_subplots "

plotly/tools.py

@@ -1087,8 +1087,8 @@ def _pad(s, cell_len=cell_len):
 
     fig = graph_objs.Figure(layout=layout)
 
-    fig['_grid_ref'] = grid_ref
-    fig['_grid_str'] = grid_str
+    fig._grid_ref = grid_ref
+    fig._grid_str = grid_str
 
     return fig