TwoKinds episode downloader

#!/usr/bin/python

# TwoKinds episode downloader
# Version 1.5
# 2014 (C) Copyright by Mrowqa, http://mrowqa.pl

import urllib2, re, glob

ARCHIVE_BASE_URL = 'http://twokinds.keenspot.com/archive.php?p='
IMG_URL_REGEX = r'http://cdn\.twokinds\.keenspot\.com/comics/[\w\-]+\.\w+'
HTTP_HEADERS = {'User-Agent': 'ponies will rule the whole world!'}
FILENAME_SCHEMA = 'twokinds_#%04d.%s'



print "Type episodes' numbers (you can use commas and dashes, for instance: 1,3-5,75,85-101): "
ids_raw = raw_input() + ","
while not re.match(r"^(\s*\d+(\s*\-\s*\d+)?\s*,)+$", ids_raw):
    print "Invalid input. Try again: "
    ids_raw = raw_input() + ","

ids = []
for number in ids_raw.split(",")[:-1]:
    number = number.split("-")
    if len(number) == 1:
        ids += [int(number[0])]
    else:
        from_id, to_id = int(number[0]), int(number[1])
        if from_id > to_id: from_id, to_id = to_id, from_id
        ids += range(from_id, to_id+1)

ids = set(ids)


print "Starting dowloading %d episodes ..." % len(ids)
downloaded_cnt = 0

for id in ids:
    print "\nID = %d" % id
    files = glob.glob(FILENAME_SCHEMA % (id, "*"))
    if files != []:
        print "Already existing files (listed below)! Skipping ...\n" + str(files)
        downloaded_cnt += 1
        continue
    url = ARCHIVE_BASE_URL + str(id)
    try:
        print "Requesting %s ..." % url
        page_content = urllib2.urlopen(url, timeout=5).read()
        images_urls = re.findall(IMG_URL_REGEX, page_content)
        if len(images_urls) != 2: # currect image + preload next
            if not ( len(images_urls) == 1 and page_content.find(ARCHIVE_BASE_URL + str(id-1)) != -1 ): # if not last image
                print "Unusual number of images (listed below). Skipping ...\n" \
                    "URLs: %s" % str(images_urls)
                continue

        img_url = images_urls[0]
        img_extension = img_url.split('.')[-1].lower()
        print "Downloading file %s ..." % img_url
        req = urllib2.Request(img_url, headers=HTTP_HEADERS)
        img_data = urllib2.urlopen(req, timeout=5).read()

        filename = FILENAME_SCHEMA % (id, img_extension)
        print "Saving image to %s ..." % filename
        file = open(filename, 'wb')
        file.write(img_data)
        file.close()

        downloaded_cnt += 1
    except Exception, e:
        print "Error occured! Message: %s" % str(e)


print "\n"*3 + "Work done!"
print "Downloaded %d episodes from %d (%.2f%%)!" % (downloaded_cnt, len(ids), float(downloaded_cnt) / len(ids) * 100.0)