Telnet.read.until function doesn't work - python-3.x

Question

Trying to telnet to a Brocade router and the python script is sending out error.... Not sure what is wrong here. Have tried a debug but cant make it working. I believe it's prompt issue. I appreciate if anyone has suggestion how to get it work.
Note: This is Python 3.0
import getpass
import sys
import telnetlib
HOST = "1.1.1.1"
user = "admin"
password = "password"
port = "23"
telnet = telnetlib.Telnet(HOST)
telnet.read_until("sw0 login:,3")
telnet.write(admin + "\r")
if password:
telnet.read_until("Password: ")
telnet.write(password + "\n")
tn.write("term len 0" + "\n")
telnet.write("sh ver br\n")
telnet.write("exit\n")
ERROR:
Traceback (most recent call last):
File "C:\Users\milan\Desktop\telnetNew.py", line 13, in <module>
telnet.read_until("Username :,3")
File "C:\Python33\lib\telnetlib.py", line 299, in read_until
return self._read_until_with_select(match, timeout)
File "C:\Python33\lib\telnetlib.py", line 352, in _read_until_with_select
i = self.cookedq.find(match)
TypeError: Type str doesn't support the buffer API
This is my prompt after logging manually using telnet port 23 and this is what i expected command to work.
_________________________________________________________________________________
Network OS (sw0)
xxxxxxxxxx
sw0 login: xxxxx
Password: xxxxx
WARNING: The default password of 'admin' and 'user' accounts have not been changed.
Welcome to the Brocade Network Operating System Software
admin connected from 10.100.131.18 using console on sw0
sw0# sh ver
sw0#

Answer 1

In looking at the docs, it appears that telnetlib want a bytestr, not a Str. so try this., which should convert everything to bytes as opposed to Str
import sys
import telnetlib
HOST = "1.1.1.1"
user = "admin"
password = "password"
port = "23"
telnet = telnetlib.Telnet(HOST,port)
telnet.read_until(b"login: ")
telnet.write(admin.encode('ascii') + b"\n")
telnet.read_until(b"Password: ")
telnet.write(password.encode('ascii') + b"\n")
tn.write(b"term len 0\n")
telnet.write(b"sh ver br\n")
telnet.write(b"exit\n")
--edit-- I installed python and tried this against one of my routers. Changing the username/password to my credentials I was able to login fine. ( I removed the password check and the getpass as they where not being used, being that your code has them hardcoded). It looks like you copied the 2.x example, but the 3.x requires the buffer compatible ones without the b" i Get this
Traceback (most recent call last):
File "foo.py", line 5, in <module>
telnet.read_until("login: ")
File "/usr/local/Cellar/python32/3.2.5/Frameworks/Python.framework/Versions/3.2/lib/python3.2/telnetlib.py", line 293, in read_until
return self._read_until_with_poll(match, timeout)
File "/usr/local/Cellar/python32/3.2.5/Frameworks/Python.framework/Versions/3.2/lib/python3.2/telnetlib.py", line 308, in _read_until_with_poll
i = self.cookedq.find(match)
TypeError: expected an object with the buffer interface
with the b" I get
[~] /usr/local/bin/python3.2 foo.py
b'\r\n\r\nThis computer system including all related equipment, network devices\r\n(specifically including Internet access), are provided only for\r\nauthorized use. All computer
which shows it is working.. what errors are you getting now

Answer 2

import telnetlib , socket
class TELNET(object):
def __init__(self):
self.tn = None
self.username = "root"
self.password = "12345678"
self.host = "10.1.1.1"
self.port = 23
self.timeout = 5
self.login_prompt = b"login: "
self.password_prompt = b"Password: "
def connect(self):
try :
self.tn = telnetlib.Telnet(self.host,self.port,self.timeout)
except socket.timeout :
print("TELNET.connect() socket.timeout")
self.tn.read_until(self.login_prompt, self.timeout)
self.tn.write(self.username.encode('ascii') + b"\n")
if self.password :
self.tn.read_until(self.password_prompt,self.timeout)
self.tn.write(self.password.encode('ascii') + b"\n")
def write(self,msg):
self.tn.write(msg.encode('ascii') + b"\n")
return True
def read_until(self,value):
return self.tn.read_until(value)
def read_all(self):
try :
return self.tn.read_all().decode('ascii')
except socket.timeout :
print("read_all socket.timeout")
return False
def close(self):
self.tn.close()
return True
def request(self,msg):
self.__init__()
self.connect()
if self.write(msg) == True :
self.close()
resp = self.read_all()
return resp
else :
return False
telnet = TELNET()
#call request function
resp = telnet.request('ps www') # it will be return ps output
print(resp)
That code works on python3

Answer 3

Most of these answers are great in-depth explanations and I found them a little hard to follow. The short answer is that the Sample code is wrong on the Python 3x site.
to fix this, instead of
' telnet.read_until("Username :,3")'
use
' telnet.read_until(b"Username :,3")'

Answer 4

Like the other answers say, the problem is that Telnetlib expects byte strings. In Python 2 the str type is a byte string (a string of binary data) whereas it's a unicode string in Python 3 and a new bytes type that represents binary data in the same was as str did in Python 2.
The upshot of this is that you need to convert your str data into bytes data when using Telnetlib in Python 3. I have some code that works in both Python2 and Python3 that I thought worth sharing.
class Telnet(telnetlib.Telnet,object):
if sys.version > '3':
def read_until(self,expected,timeout=None):
expected = bytes(expected, encoding='utf-8')
received = super(Telnet,self).read_until(expected,timeout)
return str(received, encoding='utf-8')
def write(self,buffer):
buffer = bytes(buffer, encoding='utf-8')
super(Telnet,self).write(buffer)
def expect(self,list,timeout=None):
for index,item in enumerate(list):
list[index] = bytes(item, encoding='utf-8')
match_index, match_object, match_text = super(Telnet,self).expect(list,timeout)
return match_index, match_object, str(match_text, encoding='utf-8')
You then instantiate the new Telnet class instead of telnetlib.Telnet. The new class overrides methods in Telnetlib to perform conversion from str to bytes and bytes to str so that the problem just goes away.
Of course, I've only overriden the methods that I was using, but it should be clear from the example how to extend the idea to other methods. Basically, you need to use
bytes(str_string, encoding='utf-8')
and
str(bytes_string, encoding='utf-8')
My code is valid Python 2 and 3 so will work unmodified with either interpreter. When in Python2 the code that overrides the methods is skipped over, effectively ignored. If you don't care for backwards compatibility you can remove the condition that checks for the Python version.