Return a default value instead

libs/langgraph/langgraph/graph/state.py

@@ -44,7 +44,7 @@ from langgraph.pregel.read import ChannelRead, PregelNode
 from langgraph.pregel.types import All, RetryPolicy
 from langgraph.pregel.write import SKIP_WRITE, ChannelWrite, ChannelWriteEntry
 from langgraph.store.base import BaseStore
-from langgraph.utils import RunnableCallable, coerce_to_runnable, field_is_optional
+from langgraph.utils import RunnableCallable, coerce_to_runnable, get_field_default
 
 logger = logging.getLogger(__name__)
 
@@ -492,13 +492,11 @@ class CompiledStateGraph(CompiledGraph):
                         k: (
                             self.channels[k].UpdateType,
                             (
-                                None
-                                if field_is_optional(
+                                get_field_default(
                                     k,
                                     self.channels[k].UpdateType,
                                     self.builder.input,
                                 )
-                                else ...
                             ),
                         )
                         for k in self.builder.schemas[self.builder.input]

libs/langgraph/langgraph/utils.py

@@ -246,8 +246,8 @@ def _is_readonly_type(type_: Any) -> bool:
 _DEFAULT_KEYS = frozenset()
 
 
-def field_is_optional(name: str, type_: Any, schema: Type[Any]) -> bool:
-    """Determine if the field is optional for a graph's input.
+def get_field_default(name: str, type_: Any, schema: Type[Any]) -> Any:
+    """Determine the default value for a field in a state schema.
 
     This is based on:
         If TypedDict:
@@ -259,13 +259,15 @@ def field_is_optional(name: str, type_: Any, schema: Type[Any]) -> bool:
     if name in optional_keys:
         # Either total=False or explicit NotRequired.
         # No type annotation trumps this.
-        return True
+        return None
     if _is_required_type(type_):
         # Handle Required[<type>]
         # (we already handled NotRequired and total=False)
-        return False
+        return ...
     # Note, we ignore ReadOnly attributes,
     # as they don't make much sense. (we don't care if you mutate the state in your node)
     # and mutating state in your node has no effect on our graph state.
     # Base case is the annotation
-    return _is_optional_type(type_)
+    if _is_optional_type(type_):
+        return None
+    return ...

libs/langgraph/tests/test_utils.py

@@ -23,7 +23,7 @@ from langgraph.graph import END, StateGraph
 from langgraph.graph.graph import CompiledGraph
 from langgraph.utils import (
     _is_optional_type,
-    field_is_optional,
+    get_field_default,
     is_async_callable,
     is_async_generator,
 )
@@ -200,17 +200,17 @@ def test_is_required():
         val_10: str
 
     annos = MyBaseTypedDict.__annotations__
-    assert not field_is_optional("val_1", annos["val_1"], MyBaseTypedDict)
-    assert not field_is_optional("val_2", annos["val_2"], MyBaseTypedDict)
-    assert field_is_optional("val_3", annos["val_3"], MyBaseTypedDict)
-    assert field_is_optional("val_4", annos["val_4"], MyBaseTypedDict)
+    assert get_field_default("val_1", annos["val_1"], MyBaseTypedDict) == ...
+    assert get_field_default("val_2", annos["val_2"], MyBaseTypedDict) == ...
+    assert get_field_default("val_3", annos["val_3"], MyBaseTypedDict) is None
+    assert get_field_default("val_4", annos["val_4"], MyBaseTypedDict) is None
     # See https://peps.python.org/pep-0655/#interaction-with-annotated
-    assert field_is_optional("val_5", annos["val_5"], MyBaseTypedDict)
-    assert field_is_optional("val_6", annos["val_6"], MyBaseTypedDict)
-    assert not field_is_optional("val_7", annos["val_7"], MyBaseTypedDict)
-    assert not field_is_optional("val_8", annos["val_8"], MyBaseTypedDict)
-    assert field_is_optional("val_9", annos["val_9"], MyBaseTypedDict)
-    assert not field_is_optional("val_10", annos["val_10"], MyBaseTypedDict)
+    assert get_field_default("val_5", annos["val_5"], MyBaseTypedDict) is None
+    assert get_field_default("val_6", annos["val_6"], MyBaseTypedDict) is None
+    assert get_field_default("val_7", annos["val_7"], MyBaseTypedDict) == ...
+    assert get_field_default("val_8", annos["val_8"], MyBaseTypedDict) == ...
+    assert get_field_default("val_9", annos["val_9"], MyBaseTypedDict) is None
+    assert get_field_default("val_10", annos["val_10"], MyBaseTypedDict) == ...
 
     class MyChildDict(MyBaseTypedDict):
         val_11: int
@@ -223,9 +223,9 @@ def test_is_required():
 
     cannos = MyChildDict.__annotations__
     gcannos = MyGrandChildDict.__annotations__
-    assert not field_is_optional("val_11", cannos["val_11"], MyChildDict)
-    assert field_is_optional("val_11b", cannos["val_11b"], MyChildDict)
-    assert field_is_optional("val_11c", cannos["val_11c"], MyChildDict)
-    assert field_is_optional("val_12", gcannos["val_12"], MyGrandChildDict)
-    assert field_is_optional("val_9", gcannos["val_9"], MyGrandChildDict)
-    assert not field_is_optional("val_13", gcannos["val_13"], MyGrandChildDict)
+    assert get_field_default("val_11", cannos["val_11"], MyChildDict) == ...
+    assert get_field_default("val_11b", cannos["val_11b"], MyChildDict) is None
+    assert get_field_default("val_11c", cannos["val_11c"], MyChildDict) is None
+    assert get_field_default("val_12", gcannos["val_12"], MyGrandChildDict) is None
+    assert get_field_default("val_9", gcannos["val_9"], MyGrandChildDict) is None
+    assert get_field_default("val_13", gcannos["val_13"], MyGrandChildDict) == ...