Google Developers docs image downloader.

run.py

import urllib2
from bs4 import BeautifulSoup
import urllib
import os
import sys
import Queue
import threading
import logging
import time

logging.basicConfig(format='%(asctime)s %(levelname)s %(message)s',
                    filename='log.txt', mode='a', level=logging.DEBUG)


def update_picture(url, attempt=None):
  if attempt is None:
    attempt = 1
  if attempt > 5:
    logging.error('Download of %s failed after %s attempts.', url, attempt)
    return
  print 'Checking picture %s...' % url

  try:
    img = urllib.urlopen(url).read()
  except (urllib2.HTTPError, urllib2.URLError, IOError):
    print 'error'
    update_picture(url, attempt=attempt + 1)

  fname = url.replace('/', '-').replace(':', '-').replace('--', '-')

  if os.path.isfile(fname):
    with open(fname, 'r') as old:
      old = old.read()
    if old != img:
      logging.critical('Image updated: %s' % url)
      with open(fname, 'wb') as new:
        new.write(img)
  else:
    logging.critical('New image found: %s' % url)
    with open(fname, 'wb') as new:
      new.write(img)


def parse(url='https://developers.google.com/appengine', base='https://developers.google.com/appengine'):
  print 'Parsing: %s' % url
  try:
    c = urllib2.urlopen(url)
  except (urllib2.HTTPError, urllib2.URLError, IOError):
    print 'error'
    return

  content = c.read()
  s4 = BeautifulSoup(content, 'html.parser')

  for link in s4.findAll('a', href=True):
    if link['href'].startswith('/'):
      link['href'] = 'https://developers.google.com' + link['href']
    if link['href'].startswith(url) and link['href'] != url:
      parse(link['href'], base=base)

  for image in s4.findAll('img', src=True):
    if image['src'].startswith('/'):
      image['src'] = 'https://developers.google.com' + image['src']

    if image['src'].startswith(base):
      update_picture(image['src'])

while True:

  urls = [
    'https://developers.google.com/appengine',
    'https://developers.google.com/glass/',
    'https://developers.google.com/bigquery/',
    'https://developers.google.com/datastore/',
    'https://developers.google.com/cloud-dns/',
    'https://developers.google.com/compute/',
    'https://developers.google.com/cloud-sql/',
    'https://developers.google.com/storage/',
    'https://developers.google.com/prediction/',
    'https://developers.google.com/translate/',
    'https://developers.google.com/mobile/',
    'https://developers.google.com/startups/',
    'https://developers.google.com/games/',
    'https://developers.google.com/webmasters/',
    'https://developers.google.com/chrome/',
    'https://developers.google.com/advertise/',
    'https://developers.google.com/monetize/',
    'https://developers.google.com/cloud/',
    'https://developers.google.com/+/',
    'https://developers.google.com/google-apps/',
    'https://developers.google.com/android/',
    'https://developers.google.com/tv/',
    'https://developers.google.com/wallet/',
    'https://developers.google.com/analytics/',
    'https://developers.google.com/youtube/',
    'https://developers.google.com/international/',
    'https://developers.google.com/maps/',
    'https://developers.google.com/freebase/',
    'https://developers.google.com/oauthplayground/',
    'https://developers.google.com/orkut/',
    'https://developers.google.com/kml/',
    'https://developers.google.com/experts/',
    'https://developers.google.com/eclipse/',
    'https://developers.google.com/chart/',
    'https://developers.google.com/loader/',
    'https://developers.google.com/cast/',
    'https://developers.google.com/genomics/',
    'https://developers.google.com/gdata/',
    'https://developers.google.com/discovery/',
    'https://developers.google.com/speed/',
    'https://developers.google.com/places/',
    'https://developers.google.com/v8/',
    'https://developers.google.com/blogger/',
    'https://developers.google.com/accounts/',
    'https://developers.google.com/fusiontables/',
    'https://developers.google.com/octane/',
    'https://developers.google.com/earth/',
    'https://developers.google.com/transit/',
    'https://developers.google.com/gadgets/',
    'https://developers.google.com/fonts/',
    'https://developers.google.com/recaptcha/',
    'https://developers.google.com/picker/',
    'https://developers.google.com/feed/',
    'https://developers.google.com/coordinate/',
    'https://developers.google.com/spectrum/',
    'https://developers.google.com/games/',
    'https://developers.google.com/adwords/api/',
    'https://developers.google.com/console/help/',
    'https://developers.google.com/wallet/objects/',
    'https://developers.google.com/maps-engine/',
    'https://developers.google.com/identity-toolkit/',
    'https://developers.google.com/drive/',
    'https://developers.google.com/doubleclick-publishers/',
    'https://developers.google.com/custom-search/',
    'https://developers.google.com/civic-information/',
    'https://developers.google.com/cloud-print/',
    'https://developers.google.com/public-data/',
    'https://developers.google.com/webmaster-tools/',
    'https://developers.google.com/virtual-keyboard/',
    'https://developers.google.com/shopping-content/',
    'https://developers.google.com/igoogle-themes/',
    'https://developers.google.com/translator-toolkit/',
  ]

  urls = list(set(urls))

  for url in urls:
    print parse(url, url)
    # t = threading.Thread(target=parse, args=(url, url))
    # t.daemon = True
    # t.start()
  print 'Finished...'
  time.sleep(5)

you may want to add developer.android.com to the list....