sending data across two programs in python

Question

This is my code:

socketcheck.py

import time
import subprocess

subprocess.Popen(["python", "server.py"])

for i in range(10):
    time.sleep(2)
    print i

def print_from_server(data):
    print data

server.py

import socket
from socketcheck import print_from_server

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

s.bind(('localhost',3005))

client_connected = 1

while 1:
    s.listen(1)
    conn, addr = s.accept()
    data = conn.recv(1024)
    if data:
        client_connected = 0
    else: break
    if client_connected == 0:
        print 'data received'
        print_from_server(data)
        client_connected = 1
    conn.sendall(data)

client.py

import socket

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(('localhost',3005))
s.sendall('Hello, world')
data = s.recv(1024)
#s.close()
print 'Received', repr(data)

What I am trying to do here is, run socketcheck.py which runs server.py in background and listens for a client connection. So whatever data the client sends, I want to pass it on to socketcheck.py. Is this valid? If so, then how do I achieve it?

Now when I try and run socketcheck.py, the for loop is running indefinitely.

Thanks :)

EDIT:

This initially I tried as a single program, but until the client gets connected, the rest of the program doesn't execute(blocking), with the setblocking(0) the program flow wouldn't stop but when the client connects to server it doesn't print(do anything). The server code looked something like this:

import socket from socketcheck import print_from_server

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

s.bind(('localhost',3005))
s.setblocking(0)

while 1:
    try:
        s.listen(1)
        conn, addr = s.accept()
        conn.setblocking(0)
        data = conn.recv(1024)
        if not data: break
        print 'data received'
        conn.sendall(data)
    except:
        print 'non blocking'
print 'the lengthy program continues from here'

Answer 1

The reason why your program crashes your computer is simple: You have a while loop which calls print_from_server(data), and each time it calls it, a new subprocess gets created via subprocess.Popen(["python", "server.py"]).

The reason for creating a new popen each time is a bit more complicated: You open a new server.py program in socketcheck.py. If this new server.py program calls print_from_server(data), this is the first time print_from_server(data) gets called (for the new server.py program). So the global commands (such as popen) are executed, since they are always executed once.

The number of processes running will explode quickly and you computer crashes.

One additional remark: You cannot print to console with a print command in a subprocess, since there is no console attached to that subprocess, you can only print to file. If you do that, you'll see that this output explodes quickly from all the processes.

Put socketcheck.py and server.py into one program and everything works fine, or explain why you need two programs.