class_docstr: A specific iterator for reading trees from a tree file
  
  The idea is that this will keep track of which line
  we are processing, so that an error can be logged
  from the correct line
class_docstr_tok: ["A","specific","iterator","for","reading","trees","from","a","tree","file","The","idea","is","that","this","will","keep","track","of","which","line","we","are","processing",",","so","that","an","error","can","be","logged","from","the","correct","line"]
code: def get_mark(self):
      if self.mark is None:
          raise ValueError("No mark set!")
      return self.mark
  
imports: from collections import deque
  import logging
  import os
  import re
  from stanza.models.constituency.parse_tree import Tree
  from stanza.utils.get_tqdm import get_tqdm
label_desc: Use image node_id 3 for calling the TokenIterator obj's underlying member method code with example usage: obj.get_mark() and returns: self