class_docstr: Class for tracking options.
  
  Functions like a dict, but allows us to track the history of arguments as they are
  set.
class_docstr_tok: ["Class","for","tracking","options",".","Functions","like","a","dict",",","but","allows","us","to","track","the","history","of","arguments","as","they","are","set","."]
docstr: Display the history for an item in the dict.
docstr_tok: ["Display","the","history","for","an","item","in","the","dict","."]
code: def display_history(self, key):
      """
      Display the history for an item in the dict.
      """
      changes = []
      i = 0
      for key_, val, loc in self.history:
          if key != key_:
              continue
          i += 1
          changes.append(f"{i}. {key} was set to {val} at:\n{loc}")
      if changes:
          return "\n".join(changes)
      else:
          return f"No history for {key}"
  
imports: from __future__ import annotations
  import copy
  import json
  import pickle
  import traceback
  import os
  import pkg_resources
  import parlai.utils.logging
  from typing import List
  from parlai.utils.io import PathManager
label_desc: Use image node_id 8 for calling the Opt obj's underlying member method code with example usage: obj.display_history(key) and returns: str, str, key