Adds kwargs to Dash.init_app()

Author: bormanjo

dash/dash.py

@@ -356,18 +356,11 @@ def __init__(
                 "assets_folder",
                 "assets_url_path",
                 "eager_loading",
-                "url_base_pathname",
-                "routes_pathname_prefix",
-                "requests_pathname_prefix",
                 "serve_locally",
                 "compress",
             ],
             "Read-only: can only be set in the Dash constructor",
         )
-        self.config.finalize(
-            "Invalid config key. Some settings are only available "
-            "via the Dash constructor"
-        )
 
         # keep title as a class property for backwards compatibility
         self.title = title
@@ -427,8 +420,23 @@ def __init__(
 
         self.logger.setLevel(logging.INFO)
 
-    def init_app(self, app=None):
+    def init_app(self, app=None, **kwargs):
         """Initialize the parts of Dash that require a flask app."""
+
+        self.config.update(kwargs)
+        self.config.set_read_only(
+            [
+                "url_base_pathname",
+                "routes_pathname_prefix",
+                "requests_pathname_prefix",
+            ],
+            "Read-only: can only be set in the Dash constructor or during init_app()",
+        )
+
+        self.config.finalize(
+            "Invalid config key. Some settings are only available "
+            "via the Dash constructor"
+        )
         config = self.config
 
         if app is not None:
@@ -438,6 +446,7 @@ def init_app(self, app=None):
             config.routes_pathname_prefix.replace("/", "_"), "dash_assets"
         )
 
+        print(assets_blueprint_name)
         self.server.register_blueprint(
             flask.Blueprint(
                 assets_blueprint_name,

tests/unit/test_configs.py

@@ -370,3 +370,19 @@ def test_title():
     assert "<title>Hello World</title>" in app.index()
     app = Dash(title="Custom Title")
     assert "<title>Custom Title</title>" in app.index()
+
+
+def test_app_delayed_config():
+    app = Dash(server=False)
+    app.init_app(app=Flask("test"), requests_pathname_prefix="/dash/")
+
+    assert app.config.requests_pathname_prefix == "/dash/"
+
+    with pytest.raises(AttributeError):
+        app.config.name = "cannot update me"
+
+
+def test_app_invalid_delayed_config():
+    app = Dash(server=False)
+    with pytest.raises(AttributeError):
+        app.init_app(app=Flask("test"), name="too late 2 update")