A Python script that checks the last-modified date of a URL against the last-modified date of a previous look at it. If the last-modified date has changed, it emails the designated address, saying so. This could be used as a cron job to periodically check for updates of any page on the internet.

check4siteupdate.py

# check for an update on a web-page, and email the user
import httplib
import sys
import pickle
from datetime import datetime
import smtplib
from email.mime.text import MIMEText
import yaml

def email_user(cur_data, email_from, email_to):
   msg = MIMEText("The URL you've been watching has been modified!\n{}".format(
      yaml.dump(cur_data, default_flow_style=False)))
   msg['Subject'] = 'Site Update Notification'
   msg['From'] = email_from
   msg['To'] = email_to
   server = smtplib.SMTP('localhost')
   server.sendmail(email_from, email_to, msg.as_string())
   server.quit()

# we must have a URL to check!
if len(sys.argv) < 2:
   print 'Please submit a URL as the first argument!'
   exit()

url = sys.argv[1]

if len(sys.argv) > 2:
   email_from = sys.argv[2]

if len(sys.argv) > 3:
   email_to = sys.argv[3]

# load any previous data from the data file.
data_file = '.check4update'
lm_data = {}
try:
   lm_data = pickle.load(open(data_file, 'rb'))
except IOError as e:
   print "Couldn't open {}: {}".format(data_file, e.strerror)
except EOFError:
   print "File loaded, but it's empty"

# separate the IP address from the URL path, then make the call...
address, url_path = sys.argv[1].split('/', 1)
url_path = '/' + url_path
print "Checking {} on {} for updates...".format(url_path, address)
c = httplib.HTTPConnection(address)
c.request('GET', url_path)
r = c.getresponse()

# get the date into a datetime object
lmd = r.getheader('last-modified')
if lmd != None:
   cur_data = { url: datetime.strptime(lmd, '%a, %d %b %Y %H:%M:%S %Z') }
else:
   print "Hmmm, no last-modified data was returned from the URL."
   print "Returned header:"
   print "----------------"
   print yaml.dump(dict(r.getheaders()), default_flow_style=False)
   print "----------------"
   exit()

# check to see if we have any previous last-modified data for this URL.
if url in lm_data:
   # is the current last-modified time newer than the stored time?
   if(cur_data[url] != lm_data[url]):
      print "Last-modified time has changed!\n   old: {}\n   new: {}".format(lm_data[url], cur_data[url])
      lm_data[url] = cur_data[url]
      email_user(cur_data)
   else:
      print "Last-modified time is the same: {}.".format(lm_data[url])
      email_user(cur_data)
else:
   # this is a new URL, so just add it to the stored data.
   print 'Adding new URL data:\n   URL: {}\n   last-modified: {}'.format(url, cur_data[url])
   lm_data.update(cur_data)

# save the current data to the data file...
try:
   pickle.dump(lm_data, open(data_file, 'wb'))
except:
   print "Couldn't save data file!"