code: def _prep(e):
          
          if 'lastupdate' in e:
              e['lastupdate'] = datetime.datetime.fromtimestamp(int(e['lastupdate']))
          for k in ['farm', 'server', 'id', 'secret']:
              if not k in e:
                  return e
          e["url"] = "https://farm%s.staticflickr.com/%s/%s_%s_b.jpg" % (e["farm"], e["server"], e["id"], e["secret"])
          return e
docs: Normalizes lastupdate to a timestamp, and constructs a URL from the embedded attributes.