Simple Python URL Tester for my Markdown files

check-urls.py

#! /usr/bin/python

###############################################################################
# URL Tester
# Version 0.2
#
# Usage:
# python check-urls.py CREDITS.md
#
# CREDITS
# Based on:
# https://github.com/derrekyoung/url-checker-python/blob/master/generic-check-urls.py
#
# https://docs.python.org/2/library/re.html
# http://docs.python-requests.org/en/master/_modules/requests/exceptions/
#
# https://stackoverflow.com/questions/1631897/python-file-slurp
# https://stackoverflow.com/questions/3437059/does-python-have-a-string-contains-substring-method
# https://stackoverflow.com/questions/6159900/correct-way-to-write-line-to-file
# https://stackoverflow.com/questions/930397/getting-the-last-element-of-a-list-in-python
#
# http://www.pythonforbeginners.com/system/python-sys-argv
# https://pythonadventures.wordpress.com/2010/10/11/chomp-functionality-in-python/
# https://programminghistorian.org/lessons/working-with-text-files
# https://www.mkyong.com/python/python-how-to-split-a-string/
###############################################################################

import re
import requests
import sys

def main():
    while True:
        print "\nURL Tester v.0.2"

        filename = sys.argv[1].split(".")
        extension = filename[-1]
        print "Output file: output." + extension + "\n"

        output_file = open("output." + extension, "w")

        with open(sys.argv[1]) as input_file:
            lines = input_file.readlines()

            for line in lines:
                if "http" not in line:
                    output_file.write(line )

                if re.match("^http", line):
                    line = line.rstrip()
                    status = "N/A"

                    try:
                        status = checkUrl(line)
                    except requests.exceptions.HTTPError:
                        status = "DOWN"
                    except requests.exceptions.ConnectionError:
                        status = "DOWN"
                    except requests.exceptions.ProxyError:
                        status = "DOWN"
                    except requests.exceptions.SSLError:
                        status = "DOWN"
                    except requests.exceptions.Timeout:
                        status = "DOWN"

                    if status != "200" or status == "DOWN":
                        print status + ' ' + line

                    if status == "200":
                        output_file.write(line + "  \n")
                        output_file.flush()

        input_file.close()
        output_file.close()

        print "\nURL Testing is finished!\n"
        exit()

def checkUrl(url):
    request = requests.get(url, timeout = 5)
    return str(request.status_code)

if __name__ == '__main__':
    main()