Fix Type Errors in Sample Code

[jkawamoto]

Motivation and Context

This PR resolves issue #355 by fixing type errors in the provided sample code.

How Has This Been Tested?

1. Copy the sample code into readme.py as follows:

from contextlib import asynccontextmanager
from collections.abc import AsyncIterator
from dataclasses import dataclass

from mcp.server.fastmcp import Context, FastMCP
from mcp.server.session import ServerSessionT


class Database:   # Replace with your actual DB type
    @classmethod
    async def connect(cls):
        return cls()

    async def disconnect(self):
        pass

    def query(self):
        return "Hello, World!"


# Create a named server
mcp = FastMCP("My App")


@dataclass
class AppContext:
    db: Database


@asynccontextmanager
async def app_lifespan(server: FastMCP) -> AsyncIterator[AppContext]:
    """Manage application lifecycle with type-safe context"""
    # Initialize on startup
    db = await Database.connect()
    try:
        yield AppContext(db=db)
    finally:
        # Cleanup on shutdown
        await db.disconnect()


# Pass lifespan to server
mcp = FastMCP("My App", lifespan=app_lifespan)


# Access type-safe lifespan context in tools
@mcp.tool()
def query_db(ctx: Context[ServerSessionT, AppContext]) -> str:
    """Tool that uses initialized resources"""
    db = ctx.request_context.lifespan_context.db
    return db.query()

2. Run uv run pyright readme.py to verify that the type errors have been resolved.

Breaking Changes

No.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

[Kludex]

Did you run this locally? I don't think this works properly.

[jkawamoto]

This resolves the Pyright / mypy errors but doesn't actually work. I’ve opened issue #357 and am currently preparing a PR to fix it.