docs: def open_file(self, file):
          """
          Adds a file to the list (and move it to the top of the list if the
          file already exists)
  
          :param file: file path to add the list of recent files.
  
          """
          files = self.get_recent_files()
          try:
              files.remove(file)
          except ValueError:
              pass
          files.insert(0, file)
          # discard old files
          del files[self.max_recent_files:]
          self.set_value('list', files)
          self.updated.emit()