code: def _expand_directive(
      self, specifier: str, directive, package_dir: Mapping[str, str]
  ):
      from setuptools.extern.more_itertools import always_iterable  # type: ignore
  
      with _ignore_errors(self.ignore_option_errors):
          root_dir = self.root_dir
          if "file" in directive:
              self._referenced_files.update(
                  always_iterable(directive["file"])
              )
              return _expand.read_files(directive["file"], root_dir)
          if "attr" in directive:
              return _expand.read_attr(
                  directive["attr"], package_dir, root_dir
              )
          raise ValueError(f"invalid `{specifier}`: {directive!r}")
      return None
  
imports: import logging
  import os
  from contextlib import contextmanager
  from functools import partial
  from typing import TYPE_CHECKING, Callable, Dict, Mapping, Optional, Set, Union
  from ..errors import FileError, InvalidConfigError
  from ..warnings import SetuptoolsWarning
  from .None import expand
  from ._apply_pyprojecttoml import _PREVIOUSLY_DEFINED, _MissingDynamic
  from ._apply_pyprojecttoml import apply
label_desc: Use image node_id 11 for calling the _ConfigExpander obj's underlying member method code with example usage: obj._expand_directive(specifier, directive, package_dir) and returns: None, _expand, _expand