langgraph: fix ismethod check in add_node (#3032)

Fixes #2893 #2965

libs/langgraph/langgraph/graph/state.py

@@ -361,7 +361,11 @@ class StateGraph(Graph):
 
         ends = EMPTY_SEQ
         try:
-            if (isfunction(action) or ismethod(getattr(action, "__call__", None))) and (
+            if (
+                isfunction(action)
+                or ismethod(action)
+                or ismethod(getattr(action, "__call__", None))
+            ) and (
                 hints := get_type_hints(getattr(action, "__call__"))
                 or get_type_hints(action)
             ):

libs/langgraph/tests/test_state.py

@@ -79,11 +79,19 @@ def test_state_schema_with_type_hint():
     def pre_foo(_) -> FooState:
         return {"foo": "bar"}
 
+    def pre_bar(_) -> FooState:
+        return {"foo": "bar"}
+
     class Foo:
         def __call__(self, state: FooState) -> OutputState:
             assert state.pop("foo") == "bar"
             return {"input_state": state}
 
+    class Bar:
+        def my_node(self, state: FooState) -> OutputState:
+            assert state.pop("foo") == "bar"
+            return {"input_state": state}
+
     graph = StateGraph(InputState, output=OutputState)
     actions = [
         complete_hint,
@@ -92,6 +100,8 @@ def test_state_schema_with_type_hint():
         miss_all_hint,
         pre_foo,
         Foo(),
+        pre_bar,
+        Bar().my_node,
     ]
 
     for action in actions:
@@ -112,7 +122,7 @@ def test_state_schema_with_type_hint():
     foo_state = FooState(foo="bar")
     for i, c in enumerate(graph.stream(input_state, stream_mode="updates")):
         node_name = get_name(actions[i])
-        if node_name == get_name(pre_foo):
+        if node_name in {"pre_foo", "pre_bar"}:
             assert c[node_name] == foo_state
         else:
             assert c[node_name] == output_state