Close persistent TCP connection in python after some seconds of inactivity

Question

I have built a simple TCP server, that runs on my Pi, that stores some data received from a GPRS module. It generally works fine, but at random intervals (some hours or even a couple of days) my python script doesn't receive any more data. I suspect that this is caused by a TCP connection that does not close properly. If I kill the script and try to run it again I get an error that the port is being used.

This is my code so far:

    from socket import * 
    import time

    HOST = ''
    PORT = 24071
    BUFFER_SIZE = 200
    b=" "
    data=" "

    s = socket(AF_INET, SOCK_STREAM)
    s.bind((HOST, PORT))

    while 1:
            s.listen(1)
            print ''
            print ''
            print ''
            mTime = time.strftime('%d-%m-%y   %H:%M:%S')
            print mTime
            print 'Port',PORT,': listening...'
            conn, addr = s.accept()
            print 'Connection address:', addr, conn
            while 1:
                    data = conn.recv(BUFFER_SIZE)
                    print "received:", data
                    if not data: break
                    if data=="start":
                            b=conn.recv(BUFFER_SIZE)
                            print "data:", b
                            if not b: break
                    if data=="check":
                            print "check!!"
                            conn.send("test")

I would like to end any persistent connections after some seconds (ex. 20s). Is there any way i could do this?