Returns the help string for a list of modules.

    Private to absl.flags package.

    Args:
      modules: List[str], a list of modules to get the help string for.
      prefix: str, a string that is prepended to each generated help line.
      include_special_flags: bool, whether to include description of
        SPECIAL_FLAGS, i.e. --flagfile and --undefok.

def _get_help_for_modules(self, modules, prefix, include_special_flags):
    """Returns the help string for a list of modules.

    Private to absl.flags package.

    Args:
      modules: List[str], a list of modules to get the help string for.
      prefix: str, a string that is prepended to each generated help line.
      include_special_flags: bool, whether to include description of
        SPECIAL_FLAGS, i.e. --flagfile and --undefok.
    """
    output_lines = []
    for module in modules:
      self._render_our_module_flags(module, output_lines, prefix)
    if include_special_flags:
      self._render_module_flags(
          'absl.flags',
          six.itervalues(_helpers.SPECIAL_FLAGS._flags()),  # pylint: disable=protected-access
          output_lines,
          prefix)
    return '\n'.join(output_lines)