Python simple socket client/server using asyncio

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The closest literal translation of the threading code would create the socket as before, make it non-blocking, and use asyncio low-level socket operations to implement the server. Here is an example, sticking to the more relevant server part (the client is single-threaded and likely fine as-is):

import asyncio, socket

async def handle_client(client):
    loop = asyncio.get_event_loop()
    request = None
    while request != 'quit':
        request = (await loop.sock_recv(client, 255)).decode('utf8')
        response = str(eval(request)) + '\n'
        await loop.sock_sendall(client, response.encode('utf8'))
    client.close()

async def run_server():
    server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    server.bind(('localhost', 15555))
    server.listen(8)
    server.setblocking(False)

    loop = asyncio.get_event_loop()

    while True:
        client, _ = await loop.sock_accept(server)
        loop.create_task(handle_client(client))

asyncio.run(run_server())

The above works, but is not the intended way to use asyncio. It is very low-level and therefore error-prone, requiring you to remember to set the appropriate flags on the socket. Also, there is no buffering, so something as simple as reading a line from the client becomes a tiresome chore. This API level is really only intended for implementors of alternative event loops, which would provide their implementation of sock_recv, sock_sendall, etc.

Asyncio’s public API provides two abstraction layers intended for consumption: the older transport/protocol layer modeled after Twisted, and the newer streams layer. In new code, you almost certainly want to use the streams API, i.e. call asyncio.start_server and avoid raw sockets. That significantly reduces the line count:

import asyncio, socket

async def handle_client(reader, writer):
    request = None
    while request != 'quit':
        request = (await reader.read(255)).decode('utf8')
        response = str(eval(request)) + '\n'
        writer.write(response.encode('utf8'))
        await writer.drain()
    writer.close()

async def run_server():
    server = await asyncio.start_server(handle_client, 'localhost', 15555)
    async with server:
        await server.serve_forever()

asyncio.run(run_server())

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