Quick python script for parsing CSV files

Parser.py

#!/usr/bin/python -tt
#Didn't you hear? The bird is the word!
#@version: 0.1
import sys

def main(filename):
    f = open(filename, "r")
    f2 = open("log.txt", "w")
    count = 0
    for line in f:
        result = parse(line)
        if not result == "null" and "  0" not in result:
            result = result + '\n'
            f2.write(result)
            count = count + 1
    count = str(count)
    message = 'Number of good lines found: %s' % count
    f2.write(message)        
    f.close()
    f2.close()

def parse(line):
    array = line.split(',')
    try:
        if array[11] is 0:
            final = "null"
            return final
    except:
        final = "null"
        return final
    duration = int(array[7]) * 1000
    duration = str(duration)
    called = clean(array[8])
    caller = clean(array[9])
    if " " in duration:
        final = "null"
        return final
    if called is "null" or caller is "null":
        final = "null"
        return final
    else:
        #final = called + "," + caller + "," + duration
        final = '%1s,%2s,%3s' % (called, caller, duration)
        final = str(final)
    return final
   
def clean(number):
    if not number:
        number = "null"
        return number
    if len(number) < 9:
        number = "null"
        return number
    if number[0:4] == "tel:":
        number = number[4:]
    if number[0:5] == "sip:":
        number = number[8:18]
    if number[0:2] == "+1":
        number = number[2:]
    if number[0] == 1:
        number = number[1:]
    if not len(number) == 10:
        number = "null"
        return number
    if number[0:3] == "700":
        number = "null"
    number = str(number)
    return number

if __name__ == '__main__':
    main(sys.argv[1])