Rebuild the docs around tested examples; shrink README.v2.md to a pitch (#2978)

docs_src/lowlevel/tutorial005.py

@@ -0,0 +1,51 @@
+from collections.abc import AsyncIterator
+from contextlib import asynccontextmanager
+from dataclasses import dataclass
+
+from mcp_types import (
+    CallToolRequestParams,
+    CallToolResult,
+    ListToolsResult,
+    PaginatedRequestParams,
+    TextContent,
+    Tool,
+)
+
+from mcp.server import Server, ServerRequestContext
+
+
+@dataclass
+class Catalog:
+    books: list[str]
+
+    def search(self, query: str) -> list[str]:
+        return [title for title in self.books if query.lower() in title.lower()]
+
+
+@asynccontextmanager
+async def lifespan(server: Server[Catalog]) -> AsyncIterator[Catalog]:
+    yield Catalog(books=["Dune", "Dune Messiah", "Children of Dune"])
+
+
+SEARCH_BOOKS = Tool(
+    name="search_books",
+    description="Search the catalog by title or author.",
+    input_schema={
+        "type": "object",
+        "properties": {"query": {"type": "string"}},
+        "required": ["query"],
+    },
+)
+
+
+async def list_tools(ctx: ServerRequestContext[Catalog], params: PaginatedRequestParams | None) -> ListToolsResult:
+    return ListToolsResult(tools=[SEARCH_BOOKS])
+
+
+async def call_tool(ctx: ServerRequestContext[Catalog], params: CallToolRequestParams) -> CallToolResult:
+    matches = ctx.lifespan_context.search((params.arguments or {})["query"])
+    text = f"Found {len(matches)} books: {', '.join(matches)}."
+    return CallToolResult(content=[TextContent(type="text", text=text)])
+
+
+server = Server("Bookshop", lifespan=lifespan, on_list_tools=list_tools, on_call_tool=call_tool)