fix(event): declare LambdaEventCallback.__code__ read-only so bound methods match the protocol

packages/reflex-base/news/7397.misc.md

@@ -0,0 +1 @@
+`LambdaEventCallback.__code__` is now declared read-only, matching bound methods such as `ClientStateVar.set_value`, whose `__code__` cannot be assigned.

packages/reflex-base/src/reflex_base/event/__init__.py

@@ -3054,7 +3054,17 @@ def __get__(self, instance: Any, owner: Any) -> Callable:
 class LambdaEventCallback(Protocol[*P]):
     """A protocol for a lambda event callback."""
 
-    __code__: types.CodeType
+    @property
+    def __code__(self) -> types.CodeType:
+        """The code object of the callback.
+
+        Read-only, so a bound method, whose ``__code__`` is a read-only view of
+        its function's, satisfies the protocol as well as a function or lambda.
+
+        Returns:
+            The code object.
+        """
+        ...
 
     @overload
     def __call__(self: "LambdaEventCallback[()]") -> Any: ...

tests/units/test_event.py

@@ -1,3 +1,4 @@
+import inspect
 import json
 import logging
 import shutil
@@ -1293,6 +1294,19 @@ def return_plain_callable_var(_v: Var[Any]) -> Any:
         )
 
 
+def test_lambda_event_callback_only_requires_a_readable_code_object():
+    """Bound methods expose a read-only ``__code__``, so the protocol must not need a settable one."""
+
+    class Handlers:
+        def on_value(self, value: str) -> None: ...
+
+    assert Handlers().on_value.__code__ is Handlers.on_value.__code__
+
+    code = inspect.getattr_static(LambdaEventCallback, "__code__")
+    assert isinstance(code, property)
+    assert code.fset is None
+
+
 def test_event_chain_create_accepts_a_tuple_of_events():
     """A tuple of events binds into the same chain as a list of them."""
     events = (_handler_with_arg()(1), rx.console_log("logged"))