chore: turn on mypy, add py.typed

Makefile

@@ -28,7 +28,7 @@ lint_diff format_diff: PYTHON_FILES=$(shell git diff --relative=langgraph_swarm/
 lint lint_diff:
 	[ "$(PYTHON_FILES)" = "" ] ||	uv run ruff format $(PYTHON_FILES) --diff
 	[ "$(PYTHON_FILES)" = "" ] ||	uv run ruff check $(PYTHON_FILES) --diff
-	# [ "$(PYTHON_FILES)" = "" ] || uv run mypy $(PYTHON_FILES)
+	[ "$(PYTHON_FILES)" = "" ] || uv run mypy $(PYTHON_FILES)
 
 format format_diff:
 	[ "$(PYTHON_FILES)" = "" ] || uv run ruff check --fix $(PYTHON_FILES)

langgraph_swarm/__init__.py

@@ -1,4 +1,9 @@
 from langgraph_swarm.handoff import create_handoff_tool
 from langgraph_swarm.swarm import SwarmState, add_active_agent_router, create_swarm
 
-__all__ = ["SwarmState", "add_active_agent_router", "create_handoff_tool", "create_swarm"]
+__all__ = [
+    "SwarmState",
+    "add_active_agent_router",
+    "create_handoff_tool",
+    "create_swarm",
+]

langgraph_swarm/handoff.py

@@ -47,7 +47,7 @@ def create_handoff_tool(
     def handoff_to_agent(
         state: Annotated[dict, InjectedState],
         tool_call_id: Annotated[str, InjectedToolCallId],
-    ):
+    ) -> Command:
         tool_message = ToolMessage(
             content=f"Successfully transferred to {agent_name}",
             name=name,
@@ -56,14 +56,19 @@ def handoff_to_agent(
         return Command(
             goto=agent_name,
             graph=Command.PARENT,
-            update={"messages": state["messages"] + [tool_message], "active_agent": agent_name},
+            update={
+                "messages": state["messages"] + [tool_message],
+                "active_agent": agent_name,
+            },
         )
 
     handoff_to_agent.metadata = {METADATA_KEY_HANDOFF_DESTINATION: agent_name}
     return handoff_to_agent
 
 
-def get_handoff_destinations(agent: CompiledStateGraph, tool_node_name: str = "tools") -> list[str]:
+def get_handoff_destinations(
+    agent: CompiledStateGraph, tool_node_name: str = "tools"
+) -> list[str]:
     """Get a list of destinations from agent's handoff tools."""
     nodes = agent.get_graph().nodes
     if tool_node_name not in nodes:
@@ -77,5 +82,6 @@ def get_handoff_destinations(agent: CompiledStateGraph, tool_node_name: str = "t
     return [
         tool.metadata[METADATA_KEY_HANDOFF_DESTINATION]
         for tool in tools
-        if tool.metadata is not None and METADATA_KEY_HANDOFF_DESTINATION in tool.metadata
+        if tool.metadata is not None
+        and METADATA_KEY_HANDOFF_DESTINATION in tool.metadata
     ]

langgraph_swarm/swarm.py

@@ -1,4 +1,4 @@
-from typing import Literal, Optional, Union, get_args, get_origin
+from typing import Literal, Optional, Union, cast, get_args, get_origin
 
 from langgraph.graph import START, MessagesState, StateGraph
 from langgraph.pregel import Pregel
@@ -30,7 +30,8 @@ def _update_state_schema_agent_names(
     # Check if the annotation is str or Optional[str]
     is_str_type = active_agent_annotation is str
     is_optional_str = (
-        get_origin(active_agent_annotation) is Union and get_args(active_agent_annotation)[0] is str
+        get_origin(active_agent_annotation) is Union
+        and get_args(active_agent_annotation)[0] is str
     )
 
     # We only update if the 'active_agent' is a str or Optional[str]
@@ -48,7 +49,7 @@ def _update_state_schema_agent_names(
 
     # If it was Optional[str], make it Optional[Literal[...]]
     if is_optional_str:
-        updated_schema.__annotations__["active_agent"] = Optional[literal_type]
+        updated_schema.__annotations__["active_agent"] = Optional[literal_type]  # noqa: UP045
     else:
         updated_schema.__annotations__["active_agent"] = literal_type
 
@@ -135,8 +136,8 @@ def add(a: int, b: int) -> int:
             msg,
         )
 
-    def route_to_active_agent(state: dict):
-        return state.get("active_agent", default_active_agent)
+    def route_to_active_agent(state: dict) -> str:
+        return cast("str", state.get("active_agent", default_active_agent))
 
     builder.add_conditional_edges(START, route_to_active_agent, path_map=route_to)
     return builder
@@ -223,8 +224,13 @@ def add(a: int, b: int) -> int:
     for agent in agents:
         builder.add_node(
             agent.name,
-            agent,
-            destinations=tuple(get_handoff_destinations(agent)),
+            # We need to update the type signatures in add_node to match
+            # the fact that more flexible Pregel objects are allowed.
+            agent,  # type: ignore[arg-type]
+            destinations=tuple(
+                # Need to update implementation to support Pregel objects
+                get_handoff_destinations(agent)  # type: ignore[arg-type]
+            ),
         )
 
     return builder

pyproject.toml

@@ -37,7 +37,7 @@ python_files = ["test_*.py"]
 python_functions = ["test_*"]
 
 [tool.ruff]
-line-length = 100
+line-length = 88
 target-version = "py310"
 
 [tool.ruff.lint]

tests/test_import.py

@@ -1,7 +1,2 @@
 def test_import() -> None:
     """Test that the code can be imported."""
-    from langgraph_swarm import (  # noqa: F401
-        add_active_agent_router,
-        create_handoff_tool,
-        create_swarm,
-    )

tests/test_swarm.py

@@ -1,12 +1,19 @@
+from collections.abc import Callable, Sequence
+from typing import TYPE_CHECKING, Any
+
 from langchain_core.callbacks.manager import CallbackManagerForLLMRun
 from langchain_core.language_models.chat_models import BaseChatModel
 from langchain_core.messages import AIMessage, BaseMessage
 from langchain_core.outputs import ChatGeneration, ChatResult
+from langchain_core.tools import BaseTool
 from langgraph.checkpoint.memory import MemorySaver
 from langgraph.prebuilt import create_react_agent
 
 from langgraph_swarm import create_handoff_tool, create_swarm
 
+if TYPE_CHECKING:
+    from langchain_core.runnables.config import RunnableConfig
+
 
 class FakeChatModel(BaseChatModel):
     idx: int = 0
@@ -21,13 +28,19 @@ def _generate(
         messages: list[BaseMessage],
         stop: list[str] | None = None,
         run_manager: CallbackManagerForLLMRun | None = None,
-        **kwargs,
+        **kwargs: Any,
     ) -> ChatResult:
         generation = ChatGeneration(message=self.responses[self.idx])
         self.idx += 1
         return ChatResult(generations=[generation])
 
-    def bind_tools(self, tools: list[any]) -> "FakeChatModel":
+    def bind_tools(
+        self,
+        tools: Sequence[dict[str, Any] | type | Callable[..., Any] | BaseTool],
+        *,
+        tool_choice: str | None = None,
+        **kwargs: Any,
+    ) -> "FakeChatModel":
         return self
 
 
@@ -80,7 +93,7 @@ def test_basic_swarm() -> None:
         ),
     ]
 
-    model = FakeChatModel(responses=recorded_messages)
+    model = FakeChatModel(responses=recorded_messages)  # type: ignore[arg-type]
 
     def add(a: int, b: int) -> int:
         """Add two numbers."""
@@ -109,9 +122,11 @@ def add(a: int, b: int) -> int:
     workflow = create_swarm([alice, bob], default_active_agent="Alice")
     app = workflow.compile(checkpointer=checkpointer)
 
-    config = {"configurable": {"thread_id": "1"}}
+    config: RunnableConfig = {"configurable": {"thread_id": "1"}}
     turn_1 = app.invoke(
-        {"messages": [{"role": "user", "content": "i'd like to speak to Bob"}]},
+        {  # type: ignore[arg-type]
+            "messages": [{"role": "user", "content": "i'd like to speak to Bob"}]
+        },
         config,
     )
 
@@ -122,7 +137,9 @@ def add(a: int, b: int) -> int:
     assert turn_1["active_agent"] == "Bob"
 
     turn_2 = app.invoke(
-        {"messages": [{"role": "user", "content": "what's 5 + 7?"}]},
+        {  # type: ignore[arg-type]
+            "messages": [{"role": "user", "content": "what's 5 + 7?"}]
+        },
         config,
     )