Fixes hash_function and error handler missing call for multi

CHANGELOG.md

@@ -7,6 +7,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 ## Added
 
 - [#2881](https://github.com/plotly/dash/pull/2881) Add outputs_list to window.dash_clientside.callback_context. Fixes [#2877](https://github.com/plotly/dash/issues/2877).
+- [#2903](https://github.com/plotly/dash/pull/2903) Add callback on_error handler, either globally on Dash init or per callback basis. Receives the exception as first argument, can return output(s) or None for `no_update`. Access to original callback context is preserved and `set_props` works inside the error handler.
 - [#2936](https://github.com/plotly/dash/pull/2936) Adds support for TypeScript 5.5+.
 - [#2789](https://github.com/plotly/dash/pull/2789) Add library loading capacity to `_allow_dynamic_callbacks`
 
@@ -17,6 +18,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - [#2896](https://github.com/plotly/dash/pull/2896) The tabIndex parameter of Div can accept number or string type. Fixes [#2891](https://github.com/plotly/dash/issues/2891)
 - [#2900](https://github.com/plotly/dash/pull/2900) Allow strings in layout list. Fixes [#2890](https://github.com/plotly/dash/issues/2890)
 - [#2908](https://github.com/plotly/dash/pull/2908) Fix when environment variables are ignored by Dash.run() at runtime. Fixes [#2902](https://github.com/plotly/dash/issues/2902)
+- [#2888](https://github.com/plotly/dash/pull/2888) Add id to dcc.Loading DOM. Fixes [#2878](https://github.com/plotly/dash/issues/2878)
+- [#2922](https://github.com/plotly/dash/pull/2922) Fix background callback hash_function when source is unavailable. Fixes [#1885](https://github.com/plotly/dash/issues/1885)
 - [#2915](https://github.com/plotly/dash/pull/2915) Fix 'AttributeError' when layout is a function that returns a list of components. Fixes [#2905](https://github.com/plotly/dash/issues/2905)
 - [#2956](https://github.com/plotly/dash/pull/2956) Add missing useEffect dependency to dcc.Loading component.
 

dash/_callback.py

@@ -512,7 +512,7 @@ def add_context(*args, **kwargs):
                             if not multi:
                                 output_value = NoUpdate()
                             else:
-                                output_value = [NoUpdate for _ in output_spec]
+                                output_value = [NoUpdate() for _ in output_spec]
                     else:
                         raise err
 

dash/long_callback/managers/__init__.py

@@ -107,8 +107,11 @@ def _make_set_props_key(key):
 
     @staticmethod
     def hash_function(fn, callback_id=""):
-        fn_source = inspect.getsource(fn)
-        fn_str = fn_source
+        try:
+            fn_source = inspect.getsource(fn)
+            fn_str = fn_source
+        except OSError:  # pylint: disable=too-broad-exception
+            fn_str = getattr(fn, "__name__", "")
         return hashlib.sha256(
             callback_id.encode("utf-8") + fn_str.encode("utf-8")
         ).hexdigest()

tests/integration/callbacks/test_arbitrary_callbacks.py

@@ -89,7 +89,7 @@ def no_output3(_):
         assert counter.value == 1
 
 
-def test_arb003_arbitrary_pages(dash_duo):
+def test_arb003_arbitrary_pages(dash_duo, clear_pages_state):
     app = Dash(use_pages=True, pages_folder="")
 
     register_page(

tests/integration/test_integration.py

@@ -366,7 +366,7 @@ def render_content(tab):
     until(lambda: '"label": 3' in dash_duo.find_element("#graph2_info").text, timeout=3)
 
 
-def test_inin027_multi_page_without_pages_folder(dash_duo):
+def test_inin027_multi_page_without_pages_folder(dash_duo, clear_pages_state):
     app = Dash(__name__, pages_folder="")
 
     # test for storing arbitrary keyword arguments: An `id` prop is defined for every page
@@ -473,7 +473,7 @@ def on_nested_click(n_clicks):
     dash_duo.wait_for_text_to_equal("#nested-output", "Clicked 1 times")
 
 
-def test_inin029_layout_as_list_with_pages(dash_duo):
+def test_inin029_layout_as_list_with_pages(dash_duo, clear_pages_state):
     app = Dash(use_pages=True, pages_folder="")
 
     dash.register_page(