code: def __str__(self):
      return " ".join(self.tag_sequence)
  
file_path: allennlp/allennlp/data/dataset_readers/dataset_utils/span_utils.py
imports: from typing import Callable, List, Set, Tuple, TypeVar, Optional
  import warnings
  from allennlp.common.checks import ConfigurationError
  from allennlp.data.tokenizers import Token
label_desc: Use image node_id 2 for calling the InvalidTagSequence obj's underlying member method code with example usage: obj.__str__() and returns: str