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

Answer 1

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.