Show error message when file cannot be loaded

daqviewer/daqviewer.py

@@ -117,25 +117,17 @@ def parse_contents(contents, filename):
     Input('upload-data', 'contents'),
     Input('upload-data', 'filename'),
 ])
-def csv_to_json(contents, name):
+def csv_to_json(contents, filename):
     if contents is not None:
-        return parse_contents(contents, name)
+        try:
+            json_data = parse_contents(contents, filename)
+        except:
+            json_data = json.dumps({'error': filename})
 
+        return json_data
 
-@app.callback(Output('output-data-upload', 'children'),
-              [Input('json-storage', 'children')])
-def read_json_data(json_data):
-    if json_data is None:
-        elements = html.Div([
-            dcc.Graph(),
-            html.Div([
-                html.Div([dcc.Graph()], className='six columns'),
-            ]),
-            html.Div()
-        ])
-
-        return elements
 
+def update_objects(json_data):
     info = json.loads(json_data)['info']
     df = pd.read_json(json.loads(json_data)['timeseries'], orient='table')
     ts = []
@@ -229,6 +221,38 @@ def read_json_data(json_data):
     return elements
 
 
+@app.callback(Output('output-data-upload', 'children'),
+              [Input('json-storage', 'children')])
+def read_json_data(json_data):
+    if json_data is None:
+        elements = html.Div([
+            dcc.Graph(),
+            html.Div([
+                html.Div([dcc.Graph()], className='six columns'),
+            ]),
+            html.Div()
+        ])
+
+    elif json.loads(json_data)['error']:
+        filename = json.loads(json_data)['error']
+        elements = html.Div([
+            dcc.Graph(figure={
+                'layout': {
+                    'title': 'Error reading {}'.format(filename)
+                }
+            }),
+            html.Div([
+                html.Div([dcc.Graph()], className='six columns'),
+            ]),
+            html.Div()
+        ])
+
+    else:
+        elements = update_objects(json_data)
+
+    return elements
+
+
 def main():
     port = 8050
     wb.open('http://localhost:{}'.format(port))