support logging to stderr in Jupyter Notebook Environments.

[grll]

Is your feature request related to a problem? Please describe.
I want to make mcp python-sdk jupyter notebook compatible. When running in a notebook environment, MCP work but do not output stderr as it does normally.

For instance in jupyter notebook:

import mcp
import os
from mcp.client.stdio import stdio_client

serverparams = mcp.StdioServerParameters(
 command="uv",
 args=["--quiet", "run", "../src/echo.py"],
 env={"UV_PYTHON": "3.12", **os.environ},
)

async with stdio_client(serverparams) as (read, write):
 async with mcp.ClientSession(read, write) as session:
 await session.initialize()
 tools = await session.list_tools()
 print(tools)

Outputs:

meta=None nextCursor=None tools=[Tool(name='echo_tool', description='Echo the input text\n\n Args:\n text (str): The text to echo\n\n Returns:\n str: The echoed text\n ', inputSchema={'properties':{'text':{'title': 'Text', 'type': 'string'}}, 'required': ['text'], 'title': 'echo_toolArguments', 'type': 'object'})]

while running the server without jupyter notebook:

❯ uv run --quiet src/echo.py
starting echo server

stderr is correctly displayed.

This is a big problem mostly because if the server is crashing or the command is wrong you have no way to know what's wrong: nothing is logged and the jupyter notebook cell just hangs.

Describe the solution you'd like
I found the culprit being the use of:

process = await anyio.open_process(
 [server.command, *server.args],
 env=server.env if server.env is not None else get_default_environment(),
 stderr=sys.stderr,
 )

In particular sys.stderr here is not working in the jupyter / ipython context. Instead I would suggest a working change as follow:

1. remove the stderr params from the process and handle process.stderr in an async function as stdout / stdin is handled.
2. to that effect, use a stderr_reader async function like the following:

 async def stderr_reader():
 assert process.stderr, "Opened process is missing stderr"
 try:
 async for line in process.stderr:
 if is_jupyter_notebook():
 print(f"\033[91m {line.decode().strip()}")
 else:
 # redirect to stderr as before
 print(line.decode().strip(), file=sys.stderr)
 except anyio.ClosedResourceError:
 await anyio.lowlevel.checkpoint()

This would result in the same behavior as before while allowing the stderr to be logged in the jupyter notebook context.

Additional context
Jupyter notebook support support is also requested for mcpadapt which bring MCP server tools in any agentic framework, as many agentic framework demonstrate usage in jupyter notebooks.
https://github.com/grll/mcpadapt

[grll]

@dsp-ant if that sounds reasonable to you happy to put together a PR

[grll]

actually another simpler solution is also just to explicitly set stderr to None:

process = await anyio.open_process(
 [server.command, *server.args],
 env=server.env if server.env is not None else get_default_environment(),
 stderr=None,
 )

[dsp-ant]

@grll Thanks for reporting this. I am curious as to 'why' jupyter notebooks have problems with capturing sys.stderr? I am open for fixes assuming they are not breaking backwards compatibility.

Notable, jupyter integration should probably rely on Logging to correctly capture and display logs. Now sadly, no server actually correctly implements this and we likely need better integration with standard logging facilities in Python.