code: def format(self, vertices):
          
          index = ' '.join(str(vertices[vn].index) for vn in self.vnames)
          com = ' '.join(self.vnames)  # for comment
          return '({0:s})  // {1:s} ({2:s})'.format(index, self.name, com)
docs: Format instance to dump
          vertices is dict of name to Vertex