code: def dfs(stack, x, fa_idx):
      for y in x.neighbors:
          if y.idx == fa_idx:
              continue
          stack.append((x, y, 1))
          dfs(stack, y, x.idx)
          stack.append((y, x, 0))
  
file_path: DIG/dig/ggraph/method/JTVAE/fast_jtnn/jtnn_dec.py
imports: import torch
  import torch.nn
  import torch.nn.functional
  from .mol_tree import MolTree, MolTreeNode
  from .chemutils import enum_assemble, set_atommap
  from .nnutils import create_var, GRU
label_desc: Use image node_id 1 for calling a global function with example usage: dfs(stack, x, fa_idx) without return types