docs: def _load_from_configs(self, filename):
      """
       Return content of file which located in configuration directory
      """
      config_filename = os.path.join(self._config_path, filename)
      if os.path.exists(config_filename):
        try:
          f = open(config_filename, 'r')
          content = ''.join(f.readlines())
          f.close()
          return content
        except Exception as err:
          raise err
      else:
        raise IOError("File not found: {}".format(config_filename))