code: def get_file_relative_path_by_id(self, id):
          
          for path, info in self.walk_files_info():
              if info['id']==id:
                  return path
          # none was found
          return None
docs: Given an id, get the corresponding file info relative path joined with file name.
  
          Parameters:
              #. id (string): The file unique id string.
  
          :Returns:
              #. relativePath (string): The file relative path joined with file name.
                 If None, it means file was not found.