A simple domain uptime checker

uptimeChecker.py

from threading import Thread
import requests
import time

with open('domains.txt') as f:
    domainList = f.readlines()
    domainList = [x.strip() for x in domainList]

#TODO: Check list for .onion domains and ignore said entries

# A temporary list used to store sites to be monitored when they are detected as "down"
sites_down = []

def site_up():
    # Function to monitor "up" time
    while True:
        for domain in domainList:
            try:
                r = requests.get(domain)
                if r.status_code == 200:
                    print('[* T1 *] %s --> HTTP 200 - URL OKAY' % str(domain))
                else:
                    print('[! T1 !] %s --> HTTP STATUS: %s - Adding URL to "Down Checker""...' % (str(domain), str(r.status_code)))
                    if domain not in sites_down:
                        sites_down.append(domain)
            except requests.ConnectionError:
                print('[! T1 !] %s --> Connection Error - Ignoring This URL For Now...' % str(domain))
                pass
        print('[* T1 *] All domains checked - Sleeping for 15 minutes...\n')
        time.sleep(900)


def site_down():
    # Function to monitor "down" time
    while True:
        time.sleep(300)
        for domain in sites_down:
            try:
                print('[! T2 !] Checking', domain, 'again...')
                r = requests.get(domain)
                if r.status_code == 200:
                    print('[* T2 *]', domain, '%s --> URL is now registering as ALIVE.\n')
                    sites_down.remove(domain)
                else:
                    print('[! T2 !] HTTP Status %s - I will check this URL again shortly...\n' % str(r.status_code))
            except requests.ConnectionError:
                print('[! T2 !] Connection Error!')
                pass


t1 = Thread(target=site_up)
t2 = Thread(target=site_down)
try:
    print('*' * 75)
    print('This script will check all URLs in domains.txt once every 15 minutes under Thread One (T1).')
    print('If a connection error occurs, the script will ignore the URL and check it again once T1 completes, '
          'and 15 minutes have elapsed.')
    print('If any HTTP response other than \'200\' is returned, the script will add the URL to a \'DOWN\' checker '
          'under Thread Two (T2)')
    print('The down checker runs every 5 minutes - Once it detects a URL has become \'ALIVE\' once more, the URL is '
          'removed from T2.')
    print('*' * 75)
    time.sleep(10)

    print('\n[***] Starting Threads...\n')

    t1.daemon = True
    t2.daemon = True
    t1.start()
    t2.start()
    while True:
        time.sleep(100)

except (KeyboardInterrupt, SystemExit):
    print('\n[!!!] Received Keyboard Interrupt - Quitting Threads...\n')
    exit()