code: def get_unused_node_types(
      node_types: List[NodeType], edge_types: List[EdgeType]
  ) -> Set[NodeType]:
      dst_node_types = set(edge_type[-1] for edge_type in edge_types)
      return set(node_types) - set(dst_node_types)
  
file_path: pytorch_geometric/torch_geometric/utils/hetero.py
imports: from typing import Dict, List, Optional, Set, Tuple, Union
  import torch
  from torch import Tensor
  from torch.nn import ParameterDict
  from torch_geometric.typing import Adj, EdgeType, NodeType, SparseTensor
  from torch_geometric.utils import is_sparse, to_edge_index
  from torch_geometric.utils.num_nodes import maybe_num_nodes_dict
label_desc: Use image node_id 2 for calling a global function with example usage: get_unused_node_types(node_types, edge_types) and returns: unknown