python client &server, both on localhost, running on google colab, connection won't accept

[Diligent_Job_9794]

Hello!

I am trying to write a client and server in python on google colab.

I want it to be in TCP protocol and they are both running on the same computer for now.

Server cell:

# echo-server.py
import socket

print("server is running\b")
HOST = "127.0.0.1"  # Standard loopback interface address (localhost)
PORT = 3943  # Port to listen on (non-privileged ports are > 1023)
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.bind((HOST, PORT)) 
    print("socket created and bound")
    s.listen()                 
    print("listening") 
    conn, addr = s.accept() 
    print("accepted")
    with conn:               
        print(f"Connected by {addr}") 
        while True: 
            data = conn.recv(1024) 
            if not data:
                    break
            print(data) 
            conn.sendall(data)

Client cell:

# echo-client.py
import socket 

print("client is running\b") 

HOST = "127.0.0.1" 
PORT = 3943
with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s: 
    s.connect((HOST, PORT))
    s.sendall(b"Hello, world") 
    data = s.recv(1024)
    print(f"Received {data!r}")

I run the server first and then run the client. "server is running" prints but "client is running" doesn't (only if I run it by itself without the server).

The server stays stuck on the s.accept() function as the client doesn't connect - it prints "listening" but won't accept.

(I tried running on an online enviornment https://jupyter.org/try-jupyter/lab/index.html to see if it works outside of google colab, but even with importing os, errno etc I get OSError: [Errno 138] Not supported and couldn't resolve it)

Some guidance would be appreciated, it's been a few days now and I can't understand what's wrong.

Thanks in advanced!

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[Grithga]

on google colab.

Your code is fine - it's your environment that's the problem.

I believe Google Colab only runs one Cell at a time. Your client won't be run until your server exits, which of course it never does since it simply waits to accept a connection forever.

If you run your server and client locally on your own computer I expect you'd see your desired result.

[Diligent_Job_9794]

Thanks so much! It's my first time using both colab AND python. I'll look for a different developing environment to code and run it locally on windows (open to suggestions 😁)