Make get_tools sync, add separate async initialize.

Author: rectalogic

pyproject.toml

@@ -29,6 +29,7 @@ dev = [
     "ruff~=0.8.0",
     "mypy~=1.13.0",
     "typing-extensions~=4.12.2",
+    "langchain-groq~=0.2.1",
 ]
 
 [project.urls]
@@ -81,4 +82,4 @@ warn_unused_ignores = true
 strict_equality = true
 no_implicit_optional = true
 show_error_codes = true
-files = "src/**/*.py"
+files = ["src/**/*.py", "tests/demo.py"]

src/langchain_mcp/toolkit.py

@@ -9,7 +9,7 @@
 import pydantic_core
 import typing_extensions as t
 from langchain_core.tools.base import BaseTool, BaseToolkit, ToolException
-from mcp import ClientSession
+from mcp import ClientSession, ListToolsResult
 
 
 class MCPToolkit(BaseToolkit):
@@ -20,25 +20,30 @@ class MCPToolkit(BaseToolkit):
     session: ClientSession
     """The MCP session used to obtain the tools"""
 
-    _initialized: bool = False
+    _tools: ListToolsResult | None = None
 
     model_config = pydantic.ConfigDict(arbitrary_types_allowed=True)
 
-    @t.override
-    async def get_tools(self) -> list[BaseTool]:  # type: ignore[override]
-        if not self._initialized:
+    async def initialize(self) -> None:
+        """Initialize the session and retrieve tools list"""
+        if self._tools is None:
             await self.session.initialize()
-            self._initialized = True
+            self._tools = await self.session.list_tools()
+
+    @t.override
+    def get_tools(self) -> list[BaseTool]:
+        if self._tools is None:
+            raise RuntimeError("Must initialize the toolkit first")
 
         return [
             MCPTool(
-                toolkit=self,
+                session=self.session,
                 name=tool.name,
                 description=tool.description or "",
                 args_schema=create_schema_model(tool.inputSchema),
             )
             # list_tools returns a PaginatedResult, but I don't see a way to pass the cursor to retrieve more tools
-            for tool in (await self.session.list_tools()).tools
+            for tool in self._tools.tools
         ]
 
 
@@ -67,19 +72,20 @@ class MCPTool(BaseTool):
     MCP server tool
     """
 
-    toolkit: MCPToolkit
+    session: ClientSession
     handle_tool_error: bool | str | Callable[[ToolException], str] | None = True
 
     @t.override
     def _run(self, *args: t.Any, **kwargs: t.Any) -> t.Any:
         warnings.warn(
-            "Invoke this tool asynchronousely using `ainvoke`. This method exists only to satisfy tests.", stacklevel=1
+            "Invoke this tool asynchronousely using `ainvoke`. This method exists only to satisfy standard tests.",
+            stacklevel=1,
         )
         return asyncio.run(self._arun(*args, **kwargs))
 
     @t.override
     async def _arun(self, *args: t.Any, **kwargs: t.Any) -> t.Any:
-        result = await self.toolkit.session.call_tool(self.name, arguments=kwargs)
+        result = await self.session.call_tool(self.name, arguments=kwargs)
         content = pydantic_core.to_json(result.content).decode()
         if result.isError:
             raise ToolException(content)

tests/conftest.py

@@ -46,6 +46,7 @@ def mcptoolkit(request):
 
 @pytest.fixture(scope="class")
 async def mcptool(request, mcptoolkit):
-    tool = (await mcptoolkit.get_tools())[0]
+    await mcptoolkit.initialize()
+    tool = mcptoolkit.get_tools()[0]
     request.cls.tool = tool
     yield tool

tests/demo.py

@@ -1,48 +1,46 @@
 # Copyright (C) 2024 Andrew Wason
 # SPDX-License-Identifier: MIT
 
-# /// script
-# requires-python = ">=3.10"
-# dependencies = [
-#     "langchain-mcp",
-#     "langchain-groq",
-# ]
-# ///
-
-
 import asyncio
 import pathlib
 import sys
+import typing as t
 
-from langchain_core.messages import HumanMessage
+from langchain_core.messages import AIMessage, BaseMessage, HumanMessage
 from langchain_core.output_parsers import StrOutputParser
+from langchain_core.tools import BaseTool
 from langchain_groq import ChatGroq
 from mcp import ClientSession, StdioServerParameters
 from mcp.client.stdio import stdio_client
 
 from langchain_mcp import MCPToolkit
 
 
+async def run(tools: list[BaseTool], prompt: str) -> str:
+    model = ChatGroq(model="llama-3.1-8b-instant", stop_sequences=None)  # requires GROQ_API_KEY
+    tools_map = {tool.name: tool for tool in tools}
+    tools_model = model.bind_tools(tools)
+    messages: list[BaseMessage] = [HumanMessage(prompt)]
+    ai_message = t.cast(AIMessage, await tools_model.ainvoke(messages))
+    messages.append(ai_message)
+    for tool_call in ai_message.tool_calls:
+        selected_tool = tools_map[tool_call["name"].lower()]
+        tool_msg = await selected_tool.ainvoke(tool_call)
+        messages.append(tool_msg)
+    return await (tools_model | StrOutputParser()).ainvoke(messages)
+
+
 async def main(prompt: str) -> None:
-    model = ChatGroq(model="llama-3.1-8b-instant")  # requires GROQ_API_KEY
     server_params = StdioServerParameters(
         command="npx",
         args=["-y", "@modelcontextprotocol/server-filesystem", str(pathlib.Path(__file__).parent.parent)],
     )
     async with stdio_client(server_params) as (read, write):
         async with ClientSession(read, write) as session:
             toolkit = MCPToolkit(session=session)
-            tools = await toolkit.get_tools()
-            tools_map = {tool.name: tool for tool in tools}
-            tools_model = model.bind_tools(tools)
-            messages = [HumanMessage(prompt)]
-            messages.append(await tools_model.ainvoke(messages))
-            for tool_call in messages[-1].tool_calls:
-                selected_tool = tools_map[tool_call["name"].lower()]
-                tool_msg = await selected_tool.ainvoke(tool_call)
-                messages.append(tool_msg)
-            result = await (tools_model | StrOutputParser()).ainvoke(messages)
-            print(result)
+            await toolkit.initialize()
+            response = await run(toolkit.get_tools(), prompt)
+            print(response)
 
 
 if __name__ == "__main__":