class telnetlib.Telnet([host[, port[, timeout]]])¶
 
    Telnet represents a connection to a Telnet server. The instance is initially not connected by default; the open() method must be used to establish a connection. Alternatively, the host name and optional port number can be passed to the constructor, to, in which case the connection to the server will be established before the constructor returns. The optional timeout parameter specifies a timeout in seconds for blocking operations like the connection attempt (if not specified, the global default timeout setting will be used).
 
   Do not reopen an already connected instance.

tn = telnetlib.Telnet(sys.argv[1])
tn.read_until("Username: " )
tn.write(usr + "\n" )
if pswd:
    tn.read_until("Password: " )
    tn.write(pswd + "\n" )
tn.write(["ping vrf ", sys.argv[2], " ", sys.argv[5], " ", "size 15000 repeat 5000 \n"])