code: def get_topologies(self, callback=None):
      
      if callback:
        self.topologies_watchers.append(callback)
      else:
        topologies_path = self.get_topologies_path()
        return filter(lambda f: os.path.isfile(os.path.join(topologies_path, f)),
                      os.listdir(topologies_path))
docs: get topologies