code: def check_singleton(cand_mol, ctr_node, nei_nodes):
      rings = [
          node
          for node in nei_nodes + [ctr_node]
          if node.mol.GetNumAtoms() > 2
      ]
      singletons = [
          node
          for node in nei_nodes + [ctr_node]
          if node.mol.GetNumAtoms() == 1
      ]
      if len(singletons) > 0 or len(rings) == 0:
          return True
  
      n_leaf2_atoms = 0
      for atom in cand_mol.GetAtoms():
          # a.GetDegree() == 1]
          nei_leaf_atoms = [
              a for a in atom.GetNeighbors() if not a.IsInRing()
          ]
          if len(nei_leaf_atoms) > 1:
              n_leaf2_atoms += 1
  
      return n_leaf2_atoms == 0
  
imports: import rdkit
  import rdkit.Chem
  from scipy.sparse import csr_matrix
  from scipy.sparse.csgraph import minimum_spanning_tree
  from collections import defaultdict
  from rdkit.Chem.EnumerateStereoisomers import EnumerateStereoisomers, StereoEnumerationOptions
  from .vocab import Vocab
label_desc: Use image node_id 16 for calling a global function with example usage: check_singleton(cand_mol, ctr_node, nei_nodes) and returns: unknown, True