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.
 
 ## Fixed
 
@@ -15,6 +16,8 @@ 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)
 
 ## [2.17.1] - 2024-06-12
 

dash/_callback.py

@@ -507,7 +507,7 @@ 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()