Update python-mcp-client sample code for MCP SDK 2.x

[lpozo]

The MCP Python SDK released 2.0 on 2026-07-28 (2.2.0 is current), renaming FastMCP to MCPServer and moving mcp.server.fastmcp.* to mcp.server.mcpserver.*. This folder's pyproject.toml allowed mcp>=1.20.0 with no upper bound, so a fresh uv sync today resolves to 2.x and the sample server dies on its first import with ModuleNotFoundError: No module named 'mcp.server.fastmcp'.

This also fixes a Windows bug that two readers reported on Build a Python MCP Client to Test Servers From Your Terminal (2025-11-24 and 2026-05-03) and that Bartosz diagnosed in the thread. The client wrapped the server process in a POSIX shell, sh -c "{sys.executable} {server_path} 2>/dev/null", purely to silence the server's stderr. On Windows, sh isn't on PATH and /dev/null doesn't exist, so stdio_client() can't spawn the subprocess and the app dumps a stacktrace. Running sys.executable directly and passing the SDK's own errlog parameter behaves the same on Windows, macOS, and Linux.

What changed

• mcp_server/mcp_server.py: FastMCP → MCPServer
• mcp_client/mcp_client.py: dropped the sh -c wrapper for sys.executable + errlog, added import os
• pyproject.toml: mcp>=1.20.0 → mcp>=2.2.0,<3
• uv.lock: regenerated

package	was	now
mcp	1.18.0	2.2.0
openai	2.6.0	3.11.0

Only the server's import and constructor needed changing. Every client-side API the tutorial teaches — ClientSession, StdioServerParameters, stdio_client(), .list_tools() / .list_prompts() / .list_resources(), and .call_tool() with result.content[0].text — is unchanged in 2.x, and the migration guide's client-side breaks (the removed cursor param, timedelta → float timeouts) don't apply because this code never used either.

Two incidental fixes: the lockfile was already out of sync before this change, pinning mcp>=1.17.0 against a pyproject that said >=1.20.0; and greeting_prompt() returned "Great {name} kindly." where the tutorial says "Greet". openai moves to 3.11.0 in the regenerated lock — I checked handlers.py's OpenAI() and .chat.completions.create() usage against it and no code change was needed.

Testing

uv run python -m mcp_client mcp_server/mcp_server.py --members lists the server's tool, prompt, and resource correctly on mcp 2.2.0, and call_tool() round-trips. The Windows path wasn't tested on a Windows machine — the fix removes the POSIX-only dependency, which is what broke.

Ran ruff format --check, ruff check, and dircheck.py locally with ruff 0.14.1 and all pass.

Related

Matches the tutorial update in CMS post 2355, a clone of 2015 that isn't published yet. Python MCP Server: Connect LLMs to Your Data has the same 2.x break with a larger blast radius, since FastMCP is that tutorial's subject — out of scope here, still needs its own fix.

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