代码求教

CODE:

#mail.py
#!/usr/bin/env python

import poplib, getpass, string, sys, pickle

host = raw_input("the hostname:")
if (len(host)) == 0:
        host = 'your host name'
        username = 'your username'
        password = 'your password'
else:
        username = raw_input("your username:")
        password = getpass.getpass()


try:
        sess = poplib.POP3(host)
        sess.user(username)
        sess.pass_(password)
except:
        print "0^0,there is an error in open connection"
        sys.exit()

nMess = sess.stat()[0]
headers = []
for i in range(1,nMess+1):
        print
        mesg = sess.top(i,0)
        print i, mesg[0]
        for j in range(len(mesg[1])):
                if mesg[1][j][0:5] == 'From:' or mesg[1][j][0:5] == 'Date:':
                        print mesg[1][j]
                        headers.append(mesg[1][j])

if nMess>0:
        print "received %i message total"%(nMess)
        d01 = open("From_dizhi.txt", 'w')
        pickle.dump(headers, d01)
        d01.close()
else:
        print "Nop ,no mail on", host, "for", username

        sess.quit()