docs: def fetch_room_ids(self, names):
          """ Fetches the ids of the rooms with the given names """
          ret = dict()
          names_set = frozenset(names)
          for d in json.loads(self.open_url(
                              'timetables?type=location'))['timetable']:
              name = d['hostKey']
              if name in names_set:
                  ret[name] = d['value'].encode('utf-8')
          return ret