[Python] Problems with streamlit using MCP client

Having issues with Streamlit, it does not seem compatible with an MCP client. Getting NotImplemented error.

This is the relevant streamlit code:

available_scripts = ["mcp_server1.py", "mcp_server2.py"]
selected_script = st.selectbox("MCP server script", available_scripts)
if st.button("Enable MCP server"):
mcp_client = MCPClient()
asyncio.run(mcp_client.connect_to_server(selected_script))


Now my MCPClient looks like this (based on MCP quickstart):

class MCPClient:
def __init__(self):
self.session: ClientSession | None = None
self.exit_stack = AsyncExitStack()

async def connect_to_server(self, server_script_path: str):
is_python = server_script_path.endswith(".py")
is_js = server_script_path.endswith(".js")
if not (is_python or is_js):
raise ValueError("Server script must be a .py or .js file")
command = "python" if is_python else "node"
server_params = StdioServerParameters(
command=command,
args=[server_script_path],
env=None
)

stdio_transport = await self.exit_stack.enter_async_context(stdio_client(server_params))
self.stdio, self.write = stdio_transport
self.session = await self.exit_stack.enter_async_context(ClientSession(self.stdio, self.write))

await self.session.initialize()

...


If I do this, I get a strange NotImplemented error. I will paste the error at the end, it looks like a streamlit thing.

What I discovered after debugging a bit is that the cause is await self.exit_stack.enter_async_context(...). If I remove everything after that and replace it with await asyncio.sleep(3), then it waits 3 seconds and does not fail.

I have looked around, but have not found a solution. I have seen somewhere to try:

import nest_asyncio
nest_asyncio.apply()


But either I am not putting it in the right place or this is not the problem, because I have seen no changes.

Please help! Any idea why it is failing?

File "C:\Users\danid\Documents\Personal\Projects\llm_chat_room\.venv\Lib\site-packages\streamlit\runtime\scriptrunner\exec_code.py", line 121, in exec_func_with_error_handling
result = func()
^^^^^^
File "C:\Users\danid\Documents\Personal\Projects\llm_chat_room\.venv\Lib\site-packages\streamlit\runtime\scriptrunner\script_runner.py", line 595, in code_to_exec
self._session_state.on_script_will_rerun(
File "C:\Users\danid\Documents\Personal\Projects\llm_chat_room\.venv\Lib\site-packages\streamlit\runtime\state\safe_session_state.py", line 68, in on_script_will_rerun
self._state.on_script_will_rerun(latest_widget_states)
File "C:\Users\danid\Documents\Personal\Projects\llm_chat_room\.venv\Lib\site-packages\streamlit\runtime\state\session_state.py", line 558, in on_script_will_rerun
self._call_callbacks()
File "C:\Users\danid\Documents\Personal\Projects\llm_chat_room\.venv\Lib\site-packages\streamlit\runtime\state\session_state.py", line 571, in _call_callbacks
self._new_widget_state.call_callback(wid)
File "C:\Users\danid\Documents\Personal\Projects\llm_chat_room\.venv\Lib\site-packages\streamlit\runtime\state\session_state.py", line 272, in call_callback
callback(*args, **kwargs)
File "C:\Users\danid\Documents\Personal\Projects\llm_chat_room\app.py", line 146, in toggle_mcp
asyncio.run(mcp_client.test(st.session_state["mcp_script"]))
File "C:\Users\danid\Documents\Personal\Projects\llm_chat_room\.venv\Lib\site-packages\nest_asyncio.py", line 30, in run
return loop.run_until_complete(task)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\danid\Documents\Personal\Projects\llm_chat_room\.venv\Lib\site-packages\nest_asyncio.py", line 98, in run_until_complete
return f.result()
^^^^^^^^^^
File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.11_3.11.2544.0_x64__qbz5n2kfra8p0\Lib\asyncio\futures.py", line 203, in result
raise self._exception.with_traceback(self._exception_tb)
File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.11_3.11.2544.0_x64__qbz5n2kfra8p0\Lib\asyncio\tasks.py", line 277, in __step
result = coro.send(None)
^^^^^^^^^^^^^^^
File "C:\Users\danid\Documents\Personal\Projects\llm_chat_room\mcp_client.py", line 52, in test
stdio_transport = await self.exit_stack.enter_async_context(stdio_client(server_params))
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.11_3.11.2544.0_x64__qbz5n2kfra8p0\Lib\contextlib.py", line 650, in enter_async_context
result = await _enter(cm)
^^^^^^^^^^^^^^^^
File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.11_3.11.2544.0_x64__qbz5n2kfra8p0\Lib\contextlib.py", line 210, in __aenter__
return await anext(self.gen)
^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\danid\Documents\Personal\Projects\llm_chat_room\.venv\Lib\site-packages\mcp\client\stdio\__init__.py", line 115, in stdio_client
process = await _create_platform_compatible_process(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\danid\Documents\Personal\Projects\llm_chat_room\.venv\Lib\site-packages\mcp\client\stdio\__init__.py", line 230, in _create_platform_compatible_process
process = await create_windows_process(command, args, env, errlog, cwd)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\danid\Documents\Personal\Projects\llm_chat_room\.venv\Lib\site-packages\mcp\client\stdio\win32.py", line 85, in create_windows_process
process = await anyio.open_process(
^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\danid\Documents\Personal\Projects\llm_chat_room\.venv\Lib\site-packages\anyio\_core\_subprocesses.py", line 190, in open_process
return await get_async_backend().open_process(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\danid\Documents\Personal\Projects\llm_chat_room\.venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 2561, in open_process
process = await asyncio.create_subprocess_exec(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.11_3.11.2544.0_x64__qbz5n2kfra8p0\Lib\asyncio\subprocess.py", line 223, in create_subprocess_exec
transport, protocol = await loop.subprocess_exec(
^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.11_3.11.2544.0_x64__qbz5n2kfra8p0\Lib\asyncio\base_events.py", line 1708, in subprocess_exec
transport = await self._make_subprocess_transport(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.11_3.11.2544.0_x64__qbz5n2kfra8p0\Lib\asyncio\base_events.py", line 503, in _make_subprocess_transport
raise NotImplementedError

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