I built an MCP server that pulls my Oura Ring data into Claude Desktop. It's a small Python project with nine tools. The part that cost the most time wasn't the tools. It was the Python.

My Mac's system Python is 3.9.6. I ended up running the server on 3.12.

3.9 Gaps

Python 3.9 reached end of life on October 31, 2025, according to the Python developer guide. The MCP quickstart for Python says Python 3.10 or higher. The current pyproject for the MCP Python SDK says 3.11 or higher. Those two numbers obviously don't match, so check the requirement for the version you actually install.

Either way, 3.9 is below both. And 3.10 reached end of life on October 1, 2026, so I'd start from 3.12, which gets security fixes into October 2028.

T* he fix *

Leave the system Python alone. Install a current one next to it, then do three things.

Create a virtual environment with the new Python. Install your server's dependencies inside it.…