class_docstr: Represents a stack of images to run through.
  
  Each element of the stack contains a list of the workers who have seen the given
  image for a given model. The stack ensures that no worker will see the same image
  twice.
class_docstr_tok: ["Represents","a","stack","of","images","to","run","through",".","Each","element","of","the","stack","contains","a","list","of","the","workers","who","have","seen","the","given","image","for","a","given","model",".","The","stack","ensures","that","no","worker","will","see","the","same","image","twice","."]
code: def load_stack(self) -> int:
      print(f"[ Loading stack from file... {self.save_path}]")
      with open(self.save_path, "r") as f:
          self.stack = json.load(f)
  
      pointer = self.get_pointer()
  
      # Check that the number of images is the same as before
      if len(self.stack) != self.num_images:
          raise ValueError(
              f"The loaded stack has {len(self.stack):d} images instead of the "
              f"desired {self.num_images:d}!"
          )
  
      # Make sure that the set of models is correct (i.e. in case we are loading in an
      # older obsolete version of the stack)
      if set(self.stack[0].keys()) == set(self.models):
          return pointer
      else:
          input_ = input(
              "\n\nWARNING: the currently saved stack has a different set of test "
              "cases than what is currently being used. Do you want to back up this "
              "stack file and stretch the stack to fit the new set of models? "
              "(y/n) "
          )
          if input_.lower().strip() == "y":
              self.save_stack_backup()
              return self.stretch_stack()
          else:
              raise ValueError("Mismatch in set of models in stack!")
  
imports: import base64
  import datetime
  import json
  import os
  import random
  import threading
  import time
  import unittest
  from io import BytesIO
  from typing import Any, Dict, Optional, Tuple
  from PIL import Image
  from parlai.core.message import Message
  from parlai.core.metrics import Metric
  from parlai.core.params import ParlaiParser
  from parlai.core.loader import load_task_module
  from parlai.crowdsourcing.utils.tests import AbstractParlAIChatTest
  from parlai.tasks.blended_skill_talk.agents import ContextGenerator
label_desc: Use image node_id 2 for calling the ImageStack obj's underlying member method code with example usage: obj.load_stack() and returns: pointer, self