code: def _process_field(self, container: dict, field: str, fn: Callable):
      if field in container:
          with _ignore_errors(self.ignore_option_errors):
              container[field] = fn(container[field])
  
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 3 for calling the _ConfigExpander obj's underlying member method code with example usage: obj._process_field(container, field, fn) without return types