>

>     print ("Getting running config from devices " + line)
    >     HOST = line.strip()
    >     tn = telnetlib.Telnet(HOST, 23, 5)
    >
    >     tn.read_until(b"Username:")
    >     tn.write(user.encode("ascii")+ b"n")
    >     if password:
    >         tn.read_until(b"Password:")
    >         tn.write(password.encode("ascii")+b"n")
    >
    >     tn.read_until(b"#")
    >     tn.write(b"conf t"+b"n")
    >     time.sleep(1)
    >     tn.write(b"hostname test"+b"n")
    >     time.sleep(1)
    >     tn.write(b"exit"+b"n")
    >     time.sleep(1)
    >     tn.write(b"terminal length 0"+b"n")
    >     time.sleep(3)
    >     tn.write(b"show run"+b"n")
    >     time.sleep(3)
    >     tn.write(b"exit"+b"n")
    >

readoutput = tn.read_all().decode('ascii')
saveoutput = open("device.txt" + HOST, "w")
saveoutput.write(readoutput)
saveoutput.close
tn.close()

Traceback (most recent call last):
  File "telnetbu.py", line 27, in <module>
    tn.read_until(b"Username:")
  File "/usr/lib/python3.5/telnetlib.py", line 311, in read_until
    selector.register(self, selectors.EVENT_READ)
  File "/usr/lib/python3.5/selectors.py", line 351, in register
    key = super().register(fileobj, events, data)
  File "/usr/lib/python3.5/selectors.py", line 237, in register
    key = SelectorKey(fileobj, self._fileobj_lookup(fileobj), events, data)
  File "/usr/lib/python3.5/selectors.py", line 224, in _fileobj_lookup
    return _fileobj_to_fd(fileobj)
  File "/usr/lib/python3.5/selectors.py", line 39, in _fileobj_to_fd
    "{!r}".format(fileobj)) from None
ValueError: Invalid file object: <telnetlib.Telnet object at 0x7fe669487080>