Select를 기반으로 Python으로 구현한 소켓 서버의 예에 대한 자세한 설명

import socket
import traceback
import select
EOL1 = b'\n\n'
EOL2 = b'\n\r\n'
socketmap = {}
r,w,e = [],[],[]
response = b'HTTP/1.0 200 OK\r\nDate: Mon, 1 Jan 1996 01:01:01 GMT\r\n'
response += b'Content-Type: text/plain\r\nContent-Length: 13\r\n\r\n'
response += b'Hello, world!'
serversocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
serversocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
serversocket.bind(('0.0.0.0', 23456))
serversocket.listen(1)
#serversocket.setblocking(0)
listening_fileno = serversocket.fileno()
socketmap[listening_fileno] = serversocket
print 'listening_fileno',listening_fileno
try:
  while True:
    r,w,e = [],[],[]
    for fd in socketmap:
      r.append(fd)
      w.append(fd)
      e.append(fd)
    r,w,e = select.select(r,w,e,1)
    for fd in r:
      request = b''
      isocket = socketmap[fd]
      if fd == listening_fileno:
        print 'accepting'
        clientsock,clientaddr = isocket.accept()
        #clientsock.setblocking(0)
        cli_fileno = clientsock.fileno()
        r.append(cli_fileno)
        w.append(cli_fileno)
        e.append(cli_fileno)
        socketmap[cli_fileno] = clientsock
      else:
        print 'reading'
        while EOL1 not in request and EOL2 not in request:
          request += isocket.recv(1024)
        print(request.decode())
    for fd in w:
      print 'writing'
      osocket = socketmap[fd]
      osocket.send(response)
    for fd in e:
      esocket = socketmap[fd]
      print 'socket close',fd
      esocket.close()
      del socketmap[fd]
    print "no data coming"
except Exception,e:
  print traceback.print_exc()
  serversocket.close()