docs: def _read_single(parser, filepath):
      """Reads a single config file into the parser, silently failing if the file
      does not exist.
  
      Args:
      parser (ConfigParser): parser to read the file into.
      filepath (str): full path to the config file.
      """
      from os import path
      global packages
      if path.isfile(filepath):
          parser.readfp(open(filepath))