def _postprocess_fn(nodes):
  """Grammar should be unambiguous, so nodes should never be > 1."""
  if len(nodes) > 1:
    raise ValueError(
        "Grammar is ambiguous for sub-tree with %s derivations:\n\n%s" %
        (len(nodes), "\n\n".join([parse_to_str(node) for node in nodes])))
  return nodes
Grammar should be unambiguous, so nodes should never be > 1.
language/compgen/nqg/tasks/spider/sql_parser.py