rename images downloaded from imgur so as to sort as in the original

imgurorder.py

#!/usr/bin/env python3

from lxml.html import html5parser as html
import requests
import os, os.path
import sys

class ImgurAlbumError(Exception): pass

def imgur_album_get(url):
    resp = requests.get(url)
    if resp.status_code != 200: raise ImgurAlbumError("got %03d status code requesting %s" % (resp.status_code, url))
    return resp.text

def get_image_order(src):
    h = html.document_fromstring(src)
    imgs = h.xpath('//html:div[@class="image"]', namespaces={'html':'http://www.w3.org/1999/xhtml'})
    if len(imgs) == 0:
        raise ImgurAlbumError("couldn't find any image id elements on the page")
    return [img.attrib['id'] for img in imgs]

def order(url, dir='.'):
    src = imgur_album_get(url)
    ids = get_image_order(src)
    for i, id in enumerate(ids, start=1):
        have_renamed = False
        for format in ('jpg', 'gif', 'png'):
            old_filename = '%s/%s.%s' % (dir, id, format)
            new_filename = '%s/%03d-%s.%s' % (dir, i, id, format)
            if os.path.isfile('%s/%s.%s' % (dir, id, format)):
                os.rename(old_filename, new_filename)
                have_renamed = True
        if not have_renamed:
            print("warning: didn't find a file for image with id %s" % id, file=sys.stderr)

if __name__ == '__main__':
    if not 1 < len(sys.argv) <= 3:
        print("imgurorder: renames files from a downloaded imgur album so as to sort correctly lexicographically", file=sys.stderr)
        print("usage: imgurorder url [dir]", file=sys.stderr)
        os._exit(1)
    url = sys.argv[1]
    dir = sys.argv[2] if len(sys.argv) > 2 else '.'
    try:
        order(url, dir)
    except Exception as err:
        print("error: %s" % err, file=sys.stderr)