Python Programming transferring files from one FTP server to another FTP server

import ftplib, sys
ftp1 = ftplib.FTP("127.0.0.1", "book", "bookpw")
ftp1.cwd("/Dir")
ftp2 = ftplib.FTP("www.holdenweb.com", "bookuser", "bookpw")
ftp2.cwd("/public")
sock1 = ftp1.transfercmd("RETR a.zip")
sock2 = ftp2.transfercmd("STOR b.zip")
flen = 0
while 1:
block = sock1.recv(1024)
if len(block) == 0:
break
flen += len(block)
while len(block) > 0:
sentlen = sock2.send(block)
block = block[sentlen:]
print "Transferred", flen, "bytes"
sock1.close()
sock2.close()
ftp1.quit()
ftp2.quit()</pre>