The telnetlib module provides a Telnet class that implements the Telnet protocol. See RFC 854 for details about the protocol. In addition, it provides symbolic constants for the protocol characters (see below), and for the telnet options. The symbolic names of the telnet options follow the definitions in arpa/telnet.h, with the leading TELOPT_ removed. For symbolic names of options which are traditionally not included in arpa/telnet.h, see the module source itself.
The symbolic constants for the telnet commands are: IAC, DONT, DO, WONT, WILL, SE (Subnegotiation End), NOP (No Operation), DM (Data Mark), BRK (Break), IP (Interrupt process), AO (Abort output), AYT (Are You There), EC (Erase Character), EL (Erase Line), GA (Go Ahead), SB (Subnegotiation Begin).
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.
This class has many read_*() methods. Note that some of them raise EOFError when the end of the connection is read, because they can return an empty string for other reasons. See the individual descriptions below.
See also
Telnet instances have the following methods:
Read until a given byte string, expected, is encountered or until timeout seconds have passed.
When no match is found, return whatever is available instead, possibly empty bytes. Raise EOFError if the connection is closed and no cooked data is available.
Read everything that can be without blocking in I/O (eager).
Raise EOFError if connection closed and no cooked data available. Return b'' if no cooked data available otherwise. Do not block unless in the midst of an IAC sequence.
Read readily available data.
Raise EOFError if connection closed and no cooked data available. Return b'' if no cooked data available otherwise. Do not block unless in the midst of an IAC sequence.
Process and return data already in the queues (lazy).
Raise EOFError if connection closed and no data available. Return b'' if no cooked data available otherwise. Do not block unless in the midst of an IAC sequence.
Return any data available in the cooked queue (very lazy).
Raise EOFError if connection closed and no data available. Return b'' if no cooked data available otherwise. This method never blocks.
Connect to a host. The optional second argument is the port number, which defaults to the standard Telnet port (23). 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 try to reopen an already connected instance.
Read until one from a list of a regular expressions matches.
The first argument is a list of regular expressions, either compiled (re.RegexObject instances) or uncompiled (byte strings). The optional second argument is a timeout, in seconds; the default is to block indefinitely.
Return a tuple of three items: the index in the list of the first regular expression that matches; the match object returned; and the bytes read up till and including the match.
If end of file is found and no bytes were read, raise EOFError. Otherwise, when nothing matches, return (-1, None, data) where data is the bytes received so far (may be empty bytes if a timeout happened).
If a regular expression ends with a greedy match (such as .*) or if more than one expression can match the same input, the results are indeterministic, and may depend on the I/O timing.
A simple example illustrating typical use:
import getpass
import telnetlib
HOST = "localhost"
user = input("Enter your remote account: ")
password = getpass.getpass()
tn = telnetlib.Telnet(HOST)
tn.read_until(b"login: ")
tn.write(user.encode('ascii') + b"\n")
if password:
tn.read_until(b"Password: ")
tn.write(password.encode('ascii') + b"\n")
tn.write(b"ls\n")
tn.write(b"exit\n")
print(tn.read_all().decode('ascii'))