code: def __str__(self):
      return (
          f"{self.content[:self.truncate_at]}"
          f"{'...' if len(self.content) > self.truncate_at else ''}"
      )
  
imports: from collections import namedtuple
  from functools import partial, wraps
  from nltk.corpus.reader.api import CategorizedCorpusReader
  from nltk.corpus.reader.plaintext import PlaintextCorpusReader
  from nltk.corpus.reader.util import concat, read_blankline_block
  from nltk.tokenize import blankline_tokenize, sent_tokenize, word_tokenize
label_desc: Use image node_id 3 for calling the MarkdownBlock obj's underlying member method code with example usage: obj.__str__() and returns: self, unknown