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feat: nullable exception handlers #5703

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feat: nullable exception handlers #5703

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ff9323d
feat: nullable exception handlers
Aug 11, 2025
5e77d17
fix: fixed validation of handlers
Aug 11, 2025
20b467f
fix: pyright fixes
Aug 11, 2025
7ceac10
fix: use is not None
Aug 13, 2025
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20 changes: 14 additions & 6 deletions reflex/app.py
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Original file line number Diff line number Diff line change
Expand Up @@ -422,14 +422,14 @@ class App(MiddlewareMixin, LifespanMixin):
_background_tasks: set[asyncio.Task] = dataclasses.field(default_factory=set)

# Frontend Error Handler Function
frontend_exception_handler: Callable[[Exception], None] = (
frontend_exception_handler: Callable[[Exception], None] | None = (
default_frontend_exception_handler
)

# Backend Error Handler Function
backend_exception_handler: Callable[
[Exception], EventSpec | list[EventSpec] | None
] = default_backend_exception_handler
backend_exception_handler: (
Callable[[Exception], EventSpec | list[EventSpec] | None] | None
) = default_backend_exception_handler

# Put the toast provider in the app wrap.
toaster: Component | None = dataclasses.field(default_factory=toast.provider)
Expand Down Expand Up @@ -1620,6 +1620,10 @@ def _validate_exception_handlers(self):
],
strict=True,
):
if handler_fn is None:
# If the handler is None, skip validation.
continue

if hasattr(handler_fn, "__name__"):
_fn_name = handler_fn.__name__
else:
Expand Down Expand Up @@ -1665,7 +1669,10 @@ def _validate_exception_handlers(self):
raise ValueError(msg)

# Check if the return type is valid for backend exception handler
if handler_domain == "backend":
if (
handler_domain == "backend"
and self.backend_exception_handler is not None
):
sig = inspect.signature(self.backend_exception_handler)
return_type = (
eval(sig.return_annotation)
Expand Down Expand Up @@ -1773,7 +1780,8 @@ async def process(
except Exception as ex:
telemetry.send_error(ex, context="backend")

app.backend_exception_handler(ex)
if app.backend_exception_handler is not None:
app.backend_exception_handler(ex)
raise


Expand Down
18 changes: 13 additions & 5 deletions reflex/state.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1742,8 +1742,11 @@ async def _as_state_update(
except Exception as ex:
state._clean()

app = prerequisites.get_and_validate_app().app
event_specs = (
prerequisites.get_and_validate_app().app.backend_exception_handler(ex)
app.backend_exception_handler(ex)
if app.backend_exception_handler
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it would be a tad better to check with is not None just in case a Var might come here, otherwise looks good!

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@adhami3310 thx, just fixed it

else None
)

if event_specs is None:
Expand Down Expand Up @@ -1880,8 +1883,12 @@ async def _process_event(
except Exception as ex:
telemetry.send_error(ex, context="backend")

app = prerequisites.get_and_validate_app().app

event_specs = (
prerequisites.get_and_validate_app().app.backend_exception_handler(ex)
app.backend_exception_handler(ex)
if app.backend_exception_handler
else None
)

yield await state._as_state_update(
Expand Down Expand Up @@ -2433,9 +2440,10 @@ def handle_frontend_exception(self, info: str, component_stack: str) -> None:
component_stack: The stack trace of the component where the exception occurred.

"""
prerequisites.get_and_validate_app().app.frontend_exception_handler(
Exception(info)
)
app = prerequisites.get_and_validate_app().app

if app.frontend_exception_handler is not None:
app.frontend_exception_handler(Exception(info))


class UpdateVarsInternalState(State):
Expand Down
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