Homework of my Python lesson, a half-duplex server-client chatting program

client.py

#!/usr/bin/env python

import socket
import time

BUFFSIZE = 1024

NS_HOST = 'localhost'
NS_PORT = 53333

S_HOST = ''
S_PORT = 0

print 'Connecting to name server...'
socketToNS = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
socketToNS.connect((NS_HOST, NS_PORT))
print 'Connected to name server.'
# tell the name server this is a server
data = 'client'
socketToNS.sendall(data)
# receive a server's address and port
data = socketToNS.recv(BUFFSIZE)
if cmp(data, 'no') == 0:
    print 'No server running.'
    exit()
else:
    args = data.split('&')
    S_HOST = args[0]
    S_PORT = int(args[1])
socketToNS.close()

socketToServer = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
socketToServer.connect((S_HOST, S_PORT))
print 'Connected'
print '(type "exit" to exit)'
f = open('chat_with_server_' + S_HOST + '_' + str(S_PORT) + '.txt', 'a')
while True:
    while True:
        data = raw_input('> ')
        if data:
            break
    socketToServer.sendall(data)
    record = 'Client@%s: %s' % (time.strftime('%H:%M:%S'), data)
    print record
    f.write(record + '\n')
    if cmp(data, 'exit') == 0:
        break;

    data = socketToServer.recv(BUFFSIZE)
    record = 'Server@%s: %s' % (time.strftime('%H:%M:%S'), data)
    print record
    f.write(record + '\n')
    if cmp(data, 'exit') == 0:
        break;
f.close()
socketToServer.close()

nameserver.py

#!/usr/bin/env python

import socket

BUFFSIZE = 1024

HOST = 'localhost'
PORT = 53333

servers = []

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((HOST, PORT))
while True:
    print 'Waiting for connection...'
    s.listen(1)
    conn, addr = s.accept()
    print 'Connection from', addr

    # get the type
    data = conn.recv(BUFFSIZE)
    if cmp(data, 'server') == 0:
        # a server
        print 'New server connected.'
        data = conn.recv(BUFFSIZE)
        servers.append(data)
    else:
        # a client
        print 'New client connected.'
        if len(servers) == 0:
            print 'But no server is running.'
            data = 'no'
            conn.sendall(data)
        else:
            data = servers.pop(0)
            conn.sendall(data)
            print 'Assigned server', data, 'to client.'

    conn.close()
s.close()

server.py

#!/usr/bin/env python

import socket
import time

BUFFSIZE = 1024

HOST = ''
PORT = 0

NS_HOST = 'localhost'
NS_PORT = 53333

print 'Starting server...'
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((HOST, PORT))
S_HOST, S_PORT = s.getsockname()

print 'Connecting to name server...'
socketToNS = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
socketToNS.connect((NS_HOST, NS_PORT))
print 'Connected to name server.'
# tell the name server this is a server
data = 'server'
socketToNS.sendall(data)
# send this server's address and port
data = socket.gethostbyname(socket.gethostname()) + '&' + str(S_PORT)
socketToNS.sendall(data)
socketToNS.close()
print 'Address and port sent to name server.'

print 'Waiting for client...'
s.listen(1)
conn, addr = s.accept()
print 'Connected by', addr
print '(type "exit" to exit)'
f = open('chat_with_client_' + addr[0] + '_' + str(addr[1]) + '.txt', 'a')
while True:
    data = conn.recv(BUFFSIZE)
    record = 'Client@%s: %s' % (time.strftime('%H:%M:%S'), data)
    print record
    f.write(record + '\n')

    if cmp(data, 'exit') == 0:
        break;

    while True:
        data = raw_input('> ')
        if data:
            break
    conn.sendall(data)
    record = 'Server@%s: %s' % (time.strftime('%H:%M:%S'), data)
    print record
    f.write(record + '\n')

    if cmp(data, 'exit') == 0:
        break;
f.close()
conn.close()
s.close()