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()