code: def listdir(directory):
      
      file_names = list()
      for filename in os.listdir(directory):
          file_path = os.path.join(directory, filename)
          if os.path.isdir(file_path):
              filename = f'{filename}{os.path.sep}'
          file_names.append(filename)
      return file_names
docs: Returns list of nested files and directories for local directory by path
  
      :param directory: absolute or relative path to local directory
      :return: list nested of file or directory names