use six to support python 2 and 3

ox/web/arsenalberlin.py

@@ -1,14 +1,11 @@
 # -*- coding: utf-8 -*-
 # vi:si:et:sw=4:sts=4:ts=4
-from datetime import datetime
-from urllib import urlencode
 import json
 import os
 import re
 
-from ox import find_re, strip_tags, decode_html
+from ox import find_re, strip_tags
 from ox.cache import read_url
-from ox.net import open_url
 
 def get_data(id, language='en'):
     if language == 'de':
@@ -57,7 +54,7 @@ def backup(filename):
             data = json.load(f)
     else:
         data = {}
-    start = ids and max(map(int, data)) or 1
+    start = max(map(int, data)) or 1
     for i in range(start, 11872):
         info = get_data(i)
         if info: