Python for loop: telnetlib into multiple hosts from a text file not working

I'm trying to use telnetlib to telnet into multiple devices from a text file to perform commands. When I connect to the host outside of the for loop, it works fine, but when I put it all in the for loop I get the following error:

Traceback (most recent call last):
  File "telnettest.py", line 16, in <module>
    tn = telnetlib.Telnet(HOST)
  File "/usr/local/lib/python3.6/telnetlib.py", line 218, in __init__
    self.open(host, port, timeout)
  File "/usr/local/lib/python3.6/telnetlib.py", line 234, in open
    self.sock = socket.create_connection((host, port), timeout)
  File "/usr/local/lib/python3.6/socket.py", line 704, in create_connection
    for res in getaddrinfo(host, port, 0, SOCK_STREAM):
  File "/usr/local/lib/python3.6/socket.py", line 745, in getaddrinfo
    for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
socket.gaierror: [Errno -2] Name or service not known

My code is as follows:

import getpass
import telnetlib
import sys

user = input("Enter your Username: ")
password = getpass.getpass()
enablepassword = getpass.getpass()

hosts = open('hosts.txt', 'r')
for HOST in hosts:
    print(HOST)
    tn = telnetlib.Telnet(HOST)

    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"hostname>")
    tn.write(b"enable\n")
    tn.write(enablepassword.encode('ascii') + b"\n")
    tn.write(b"show version\n")
    tn.write(b"exit\n")
    tn.write(b"exit\n")

output = tn.read_all().decode('ascii')
print(output)

with open("telnetfile.txt", "a") as f:
    f.write(output)

Like I said, this all works fine outside of a for loop and when I've defined the HOST value without a file. However it seems to error trying to telnet, when I put it in a for loop, even though the print(HOST) prints the correct hostname. Even when there is only one host name in the file, it still errors.

Am I missing something blatantly obvious here?

Any help would be greatly appreciated.

Cheers.

You need to strip each line when opening the file. This is because the return character is included (\n) for each line.

import getpass
import telnetlib
import sys

user = input("Enter your Username: ")
password = getpass.getpass()
enablepassword = getpass.getpass()

with open('hosts.txt') as hosts:
    for HOST in hosts:
        print(HOST)
        tn = telnetlib.Telnet(HOST.strip())

        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"hostname>")
        tn.write(b"enable\n")
        tn.write(enablepassword.encode('ascii') + b"\n")
        tn.write(b"show version\n")
        tn.write(b"exit\n")
        tn.write(b"exit\n")

output = tn.read_all().decode('ascii')
print(output)

with open("telnetfile.txt", "a") as f:
    f.write(output)