code: def format_values(self):
          
          source_key_to_display_value_map = {
              _COMMAND_LINE_SOURCE_KEY: "Command Line Args: ",
              _ENV_VAR_SOURCE_KEY: "Environment Variables:\n",
              _CONFIG_FILE_SOURCE_KEY: "Config File (%s):\n",
              _DEFAULTS_SOURCE_KEY: "Defaults:\n"
          }
  
          r = StringIO()
          for source, settings in self._source_to_settings.items():
              source = source.split("|")
              source = source_key_to_display_value_map[source[0]] % tuple(source[1:])
              r.write(source)
              for key, (action, value) in settings.items():
                  if key:
                      r.write("  %-19s%s\n" % (key+":", value))
                  else:
                      if isinstance(value, str):
                          r.write("  %s\n" % value)
                      elif isinstance(value, list):
                          r.write("  %s\n" % ' '.join(value))
  
          return r.getvalue()
docs: Returns a string with all args and settings and where they came from
          (eg. commandline, config file, enviroment variable or default)