code: def extract_smiles(s):
      
      # TODO: This still gets a lot of false positives.
      smiles = []
      for t in s.split():
          if len(t) > 2 and SMILES_RE.match(t) and not t.endswith('.') and bracket_level(t) == 0:
              smiles.append(t)
      return smiles
docs: Return a list of SMILES identifiers extracted from the string.