Pick up app name from server instance (#771)

dash/CHANGELOG.md

@@ -15,6 +15,8 @@
 
 - [#739](https://github.com/plotly/dash/pull/739) Allow the Flask app to be provided to Dash after object initialization. This allows users to define Dash layouts etc when using the app factory pattern, or any other pattern that inhibits access to the app object. This broadly complies with the flask extension API, allowing Dash to be considered as a Flask extension where it needs to be.
 
+- [#774](https://github.com/plotly/dash/pull/774) Allow the Flask app to set the Dash app name if the name is not provided by users.
+
 - [#722](https://github.com/plotly/dash/pull/722) Assets are served locally by default. Both JS scripts and CSS files are affected. This improves robustness and flexibility in numerous situations, but in certain cases initial loading could be slowed. To restore the previous CDN serving, set `app.scripts.config.serve_locally = False` (and similarly with `app.css`, but this is generally less important).
 
 - Undo/redo toolbar is removed by default, you can enable it with `app=Dash(show_undo_redo=true)`. The CSS hack `._dash-undo-redo:{display:none;}` is no longer needed [#724](https://github.com/plotly/dash/pull/724)

dash/dash.py

@@ -205,7 +205,7 @@ class Dash(object):
     """
     def __init__(
             self,
-            name='__main__',
+            name=None,
             server=True,
             assets_folder='assets',
             assets_url_path='assets',
@@ -239,10 +239,13 @@ def __init__(
 
         # We have 3 cases: server is either True (we create the server), False
         # (defer server creation) or a Flask app instance (we use their server)
-        if isinstance(server, bool):
-            self.server = Flask(name) if server else None
-        elif isinstance(server, Flask):
+        if isinstance(server, Flask):
             self.server = server
+            if name is None:
+                name = getattr(server, 'name', '__main__')
+        elif isinstance(server, bool):
+            name = name if name else '__main__'
+            self.server = Flask(name) if server else None
         else:
             raise ValueError('server must be a Flask app or a boolean')
 

tests/unit/test_configs.py

@@ -1,9 +1,11 @@
 import os
 import unittest
+import pytest
+from flask import Flask
 # noinspection PyProtectedMember
 from dash._configs import (
     pathname_configs, DASH_ENV_VARS, get_combined_config, load_dash_env_vars)
-from dash import exceptions as _exc
+from dash import Dash, exceptions as _exc
 from dash._utils import get_asset_path
 
 
@@ -138,5 +140,17 @@ def test_load_dash_env_vars_refects_to_os_environ(self):
             self.assertEqual(vars[var], 'false')
 
 
+@pytest.mark.parametrize('name, server, expected', [
+    (None, True, '__main__'),
+    ('test', True, 'test'),
+    ('test', False, 'test'),
+    (None, Flask('test'), 'test'),
+    ('test', Flask('other'), 'test'),
+])
+def test_app_name_server(name, server, expected):
+    app = Dash(name=name, server=server)
+    assert app.config.name == expected
+
+
 if __name__ == '__main__':
     unittest.main()