code: def identifiers(config):
      
      ids = []
      if (config.klass_name == 'gen'):
          for generator in os.listdir(config.generator_dir):
              if (generator == '__init__.py'):
                  continue
              (gid, ext) = os.path.splitext(generator)
              if (ext == '.py' and
                      os.path.isfile(os.path.join(config.generator_dir, generator))):
                  ids.append(gid)
      else:
          for image_file in os.listdir(config.image_dir):
              (iid, ext) = os.path.splitext(image_file)
              if (ext in ['.jpg', '.png', '.tif'] and
                      os.path.isfile(os.path.join(config.image_dir, image_file))):
                  ids.append(iid)
      return ids
docs: Show list of identifiers for this prefix.
  
      Handles both the case of local file based identifiers and
      also image generators.
  
      Arguments:
          config - configuration object in which:
              config.klass_name - 'gen' if a generator function
              config.generator_dir - directory for generator code
              config.image_dir - directory for images
  
      Returns:
          ids - a list of ids