How to use the tts.load_json_file function in TTS

def file_list_has_changed(self,now):
    if not now:
      return
    ident=self.file_store[now[0]]
    filename=self.filesystem.get_json_filename_for_type(ident,self.save_type.get())
    data=tts.load_json_file(filename)
    # TODO: error handling
    self.save=tts.Save(savedata=data,
                       ident=ident,
                       filename=filename,
                       save_type=tts.SaveType(self.save_type.get()),
                       filesystem=self.filesystem)
    if self.save.isInstalled:
      self.downloadButton.configure(text="All files Downloaded",
                                    state=Tk.DISABLED)
      self.exportButton.configure(text="Export",state=Tk.NORMAL)
    else:
      self.downloadButton.configure(text="Download missing files",
                                    state=Tk.NORMAL)
      self.exportButton.configure(text="Download and Export",
                                  state=Tk.NORMAL)

def file_list_has_changed(self,now):
    if not now:
      return
    ident=self.file_store[now[0]]
    filename=self.filesystem.get_json_filename_for_type(ident,self.save_type.get())
    data=tts.load_json_file(filename)
    # TODO: error handling
    self.save=tts.Save(savedata=data,
                  ident=ident,
                  filename=filename,
                  save_type=tts.SaveType(self.save_type.get()),
                  filesystem=self.filesystem)
    if self.save.isInstalled:
      self.status_label.config(text="All files found.")
    else:
      self.status_label.config(text="Some cache files missing - check details on list page.")
    self.file_list.event_generate("<>")

filename=args.output
    else:
      filename=args.id+".pak"

    data=None
    json_filename=None
    if not args.save_type:
      args.save_type=self.filesystem.get_json_filename_type(args.id)
    if not args.save_type:
      return 1,"Unable to determine type of id %s" % args.id

    json_filename=self.filesystem.get_json_filename_for_type(args.id,args.save_type)

    if not json_filename:
      return 1, "Unable to find filename for id %s (wrong -s/-w/-c specified?)" % args.id
    data=tts.load_json_file(json_filename)
    if not data:
      return 1, "Unable to load data for file %s" % json_filename

    save=tts.Save(savedata=data,
                  filename=json_filename,
                  ident=args.id,
                  save_type=args.save_type,
                  filesystem=self.filesystem)
    if not save.isInstalled:
      if not args.download:
        return 1, "Unable to find all urls required by %s. Rerun with -d to try and download them or open it within TTS.\n%s" % (args.id,save)
      else:
        tts.logger().info("Downloading missing files...")
        successful = save.download()
        if successful:
          tts.logger().info("Files downloaded successfully.")