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()