Making a Python script Object-Oriented

I'm writing an application in Python that is going to have a lot of different functions, so logically I thought it would be best to split up my script into different modules. Currently my script reads in a text file that contains code which has been converted into tokens and spellings. The script then reconstructs the code into a string, with blank lines where comments would have been in the original code.

I'm having a problem making the script object-oriented though. Whatever I try I can't seem to get the program running the same way it would as if it was just a single script file. Ideally I'd like to have two script files, one that contains a class and function that cleans and reconstructs the file. The second script would simply call the function from the class in the other file on a file given as an argument from the command line. This is my current script:

import sys

tokenList = open(sys.argv[1], 'r')
cleanedInput = ''
prevLine = 0

for line in tokenList:

    if line.startswith('LINE:'):
        lineNo = int(line.split(':', 1)[1].strip())
        diff = lineNo - prevLine - 1

        if diff == 0:
            cleanedInput += '\n'
        if diff == 1:
            cleanedInput += '\n\n'
        else:
            cleanedInput += '\n' * diff

        prevLine = lineNo
        continue

    cleanedLine = line.split(':', 1)[1].strip()
    cleanedInput += cleanedLine + ' '

print cleanedInput

After following Alex Martelli advice below, I now have the following code which gives me the same output as my original code.

def main():
    tokenList = open(sys.argv[1], 'r')
    cleanedInput = []
    prevLine = 0

    for line in tokenList:

        if line.startswith('LINE:'):
            lineNo = int(line.split(':', 1)[1].strip())
            diff = lineNo - prevLine - 1

            if diff == 0:
                cleanedInput.append('\n')
            if diff == 1:
                cleanedInput.append('\n\n')
            else:
                cleanedInput.append('\n' * diff)

            prevLine = lineNo
            continue

        cleanedLine = line.split(':', 1)[1].strip()
        cleanedInput.append(cleanedLine + ' ')

    print cleanedInput

if __name__ == '__main__':
    main()

I would still like to split my code into multiple modules though. A 'cleaned file' in my program will have other functions performed on it so naturally a cleaned file should be a class in its own right?