Better ping/pong support

examples/ping_pong/client.py

@@ -0,0 +1,17 @@
+#!/usr/bin/env python
+
+import asyncio
+import websockets
+
+async def hello(uri):
+    async with websockets.connect(uri) as websocket:
+        await websocket.send("Hello world!")
+        response = await websocket.recv()
+        print(response)
+
+        pong_waiter = await websocket.ping('coucou')
+        ret = await pong_waiter   # only if you want to wait for the pong
+        print(ret)
+
+asyncio.get_event_loop().run_until_complete(
+    hello('ws://localhost:5678'))