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websockets is a library for building WebSocket servers and clients in Python with a focus on correctness, simplicity, robustness, and performance.

It supports several network I/O and control flow paradigms:

  1. The default implementation builds upon asyncio, Python’s standard asynchronous I/O framework. It provides an elegant coroutine-based API. It’s ideal for servers that handle many clients concurrently.

  2. The threading implementation is a good alternative for clients, especially if you aren’t familiar with asyncio. It may also be used for servers that don’t need to serve many clients.

  3. The Sans-I/O implementation is designed for integrating in third-party libraries, typically application servers, in addition being used internally by websockets.

Here’s an echo server with the asyncio API:

#!/usr/bin/env python

import asyncio
from websockets.server import serve

async def echo(websocket):
    async for message in websocket:
        await websocket.send(message)

async def main():
    async with serve(echo, "localhost", 8765):
        await asyncio.get_running_loop().create_future()  # run forever


Here’s how a client sends and receives messages with the threading API:

#!/usr/bin/env python

import asyncio
from websockets.sync.client import connect

def hello():
    with connect("ws://localhost:8765") as websocket:
        websocket.send("Hello world!")
        message = websocket.recv()
        print(f"Received: {message}")


Don’t worry about the opening and closing handshakes, pings and pongs, or any other behavior described in the WebSocket specification. websockets takes care of this under the hood so you can focus on your application!

Also, websockets provides an interactive client:

$ python -m websockets ws://localhost:8765/
Connected to ws://localhost:8765/.
> Hello world!
< Hello world!
Connection closed: 1000 (OK).

Do you like it? Let’s dive in!