Add the client-side subscriptions/listen driver (#3047)

docs_src/subscriptions/tutorial003.py

@@ -0,0 +1,30 @@
+from mcp_types import TextResourceContents
+
+from mcp import Client
+from mcp.client.subscriptions import ResourceUpdated, ToolsListChanged
+
+BOARD = "board://sprint"
+
+
+async def read_board(client: Client, uri: str = BOARD) -> str:
+    [contents] = (await client.read_resource(uri)).contents
+    assert isinstance(contents, TextResourceContents)
+    return contents.text
+
+
+async def follow_board(client: Client) -> None:
+    async with client.listen(tools_list_changed=True, resource_subscriptions=[BOARD]) as sub:
+        async for event in sub:
+            match event:
+                case ResourceUpdated(uri=uri):
+                    print(await read_board(client, uri))
+                case ToolsListChanged():
+                    tools = await client.list_tools()
+                    print("tools:", [tool.name for tool in tools.tools])
+                case _:
+                    pass  # kinds the filter did not ask for never arrive
+
+
+async def main() -> None:
+    async with Client("http://localhost:8000/mcp") as client:
+        await follow_board(client)