python-aiohttpHow to create a Python aiohttp websocket client?

Creating a Python aiohttp websocket client is relatively straightforward. The following example code creates a websocket client that connects to a websocket server and prints out any messages it receives:

import asyncio
from aiohttp import web

async def websocket_handler(request):
    ws = web.WebSocketResponse()
    await ws.prepare(request)

    async for msg in ws:
        if msg.type == web.WSMsgType.TEXT:
            if msg.data == 'close':
                await ws.close()
            else:
                print('Received:', msg.data)
        elif msg.type == web.WSMsgType.ERROR:
            print('ws connection closed with exception %s' %
                  ws.exception())

    print('websocket connection closed')

    return ws

Output example

Received: Hello
Received: World
websocket connection closed

The code consists of the following parts:

1. import asyncio and from aiohttp import web: imports the necessary libraries for the websocket client.
2. async def websocket_handler(request):: defines the websocket handler function.
3. ws = web.WebSocketResponse(): creates a websocket response object.
4. await ws.prepare(request): prepares the websocket response object.
5. async for msg in ws:: starts an asynchronous loop to receive messages from the websocket server.
6. if msg.type == web.WSMsgType.TEXT:: checks if the message type is text.
7. if msg.data == 'close':: checks if the message data is 'close'.
8. await ws.close(): closes the websocket connection.
9. else:: prints out the message data.
10. elif msg.type == web.WSMsgType.ERROR:: checks if the message type is an error.
11. print('ws connection closed with exception %s' % ws.exception()): prints out the exception.
12. print('websocket connection closed'): prints out a message when the websocket connection is closed.
13. return ws: returns the websocket response object.

Helpful links

• aiohttp Documentation
• Websockets with aiohttp

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