Using telnetlib. How to make use of a response after writing a command

Question

I am extremely new to Python and after several weeks of study and practice programming I have begun my home automation project.

My aim is to interact with a Java based service that runs on my Windows machine called C-Gate. This then interprets and communicates with the much more complicated commands sent & received by my Clipsal C-Bus automation system.

So far I have managed to create a connection to C-Gate using telnelib and write/read commands.

What I have been trying to figure out for some time now is how to use the responses given by C-Gate and extract a particular value such as the level of a light and turn it into a variable I can use.

From there I should be able to expand my understanding and begin building an interface to use/monitor these values.

Here is my code so far:

import telnetlib

HOST = "localhost"
PORT = "20023"


def read_until(cue, timeout=2):
    print tn.read_until(cue, timeout)


def tn_write(text):
    tn.write(text)


tn = telnetlib.Telnet(HOST, PORT)


tn_write('project load MYHOUSE\r\n')

read_until('200 OK.')

tn_write('project use MYHOUSE\r\n')

read_until('200 OK.')

tn_write('net open 254\r\n')

read_until('200 OK: //MYHOUSE/254')

tn_write('project start\r\n')

read_until('200 OK.')



tn_write('get 254/56/1 level\r\n')

tn_write('get 254/56/2 level\r\n')

tn_write('get 254/56/3 level\r\n')

tn_write('get 254/56/4 level\r\n')

tn_write('get 254/56/5 level\r\n')

tn_write('get 254/56/6 level\r\n')

tn_write('get 254/56/7 level\r\n')

tn_write('get 254/56/8 level\r\n')

read_until('300 //MYHOUSE/254/56/1: level=0\r\n')

This then prints the following responses:

201 Service ready: Clipsal C-Gate Version: v2.9.5 (build 2460) #cmd-syntax=1.0

200 OK.

200 OK.

200 OK: //MYHOUSE/254

200 OK.

300 //MYHOUSE/254/56/1: level=100

300 //MYHOUSE/254/56/2: level=0

300 //MYHOUSE/254/56/3: level=0

300 //MYHOUSE/254/56/4: level=0

300 //MYHOUSE/254/56/5: level=0

300 //MYHOUSE/254/56/6: level=0

300 //MYHOUSE/254/56/7: level=0

300 //MYHOUSE/254/56/8: level=0

Marcin Kowalczyk · Accepted Answer · 2013-05-25T20:48:29.390

You can perfirm this task in few ways but I would recommend using regular expression. First of all, telnet code should be modified a little bit:

def read_until(cue, timeout=2):
    return tn.read_until(cue, timeout)

telnetReturnedValue = read_until('200 OK: //MYHOUSE/254')

Example code which would extract value of "level":

import re
rePattern = 'level=(\d+)'
matchTuple = re.search(rePattern,telnetReturnedValue)
if(matchTuple!=None):
    levelValue = matchTuple.groups()[0]
    print(levelValue)

Re library documentation: http://docs.python.org/2/library/re.html .

UPDATE: Answering more detailed whittie83's question, there are many ways to write this program. It is still about Python basics so I would recommend learning from at least some tutorial, for example: http://docs.python.org/2/tutorial/.

Anyway, I would put regexp code into function like this:

import re
def parseTelnetOutput(output,rePattern='level=(\d+)'):
    print(output)
    matchTuple = re.search(rePattern,output)
    if(matchTuple!=None):
        someValue = matchTuple.groups()[0]
        return(someValue)

#telnet functions definitions and telnet initiation 

levelsList = []  #empty table for extracted levels

#some telnet commands...
tn_write('project load MYHOUSE\r\n')
print(read_until('200 OK.'))#not parsing, only printing
tn_write('net open 254\r\n')
parseResult = parseTelnetOutput(read_until('200 OK: //MYHOUSE/254/56/1'))
levelsList.append(parseResult)  # adding extracted level into a table
tn_write('net open 254\r\n')
parseResult = parseTelnetOutput(read_until('200 OK: //MYHOUSE/254/56/2'))
levelsList.append(parseResult)  # adding extracted level into a table
#etc...

for pr in levelsList:  #iterating list of extracted levels
    print(pr)

It is only a suggestion. You can merge 3 functions into 1, embed variables and functions into a class and so on. It is up to you.

Thanks Marcin. I had actually just begun playing with the re module as a solution. — whittie83, May 25 '13 at 07:10
My biggest problem now is how do I break these functions up? So that they a) complete in a sequence, like I need the first four tn_write commands to run and just initialise the server before I then ask about the levels. then b) process the responses differently as I am happy to just test and see the whole response for the first four but as demonstrated by your code I need to then extract the levels from the next lot of commands. — whittie83, May 25 '13 at 07:19
I've updated my answer and put some more code. I hope it answers your question. — Marcin Kowalczyk, May 25 '13 at 20:49
Thank you Marcin. This has been a huge help. Like you say, I do have allot to learn in order for some of it to make real sense to me but it has given me the building blocks to advance in this language. Thank you for your time and patience. I still have much to learn. — whittie83, May 27 '13 at 10:40

Using telnetlib. How to make use of a response after writing a command

1 Answers1