code: def substitute_with_template(
      self,
      template_fn: str,
      env_callable: Callable[[], Union[str, Dict[str, Any]]],
  ) -> str:
      template_path = os.path.join(self.template_dir, template_fn)
      env = env_callable()
      if isinstance(env, dict):
          # TODO: Update the comment reference to the correct location
          if "generated_comment" not in env:
              comment = "@" + "generated by torchgen/gen.py"
              comment += f" from {os.path.basename(template_path)}"
              env["generated_comment"] = comment
          template = _read_template(template_path)
          return template.substitute(env)
      elif isinstance(env, str):
          return env
      else:
          assert_never(env)
  
imports: import contextlib
  import functools
  import hashlib
  import os
  import re
  import sys
  import textwrap
  from argparse import Namespace
  from dataclasses import fields, is_dataclass
  from enum import auto, Enum
  from typing import Any, Callable, Dict, Generic, Iterable, Iterator, List, Literal, NoReturn, Optional, Sequence, Set, Tuple, TypeVar, Union
  from typing_extensions import Self
  from torchgen.code_template import CodeTemplate
label_desc: Use image node_id 3 for calling the FileManager obj's underlying member method code with example usage: obj.substitute_with_template(template_fn, env_callable) and returns: template, env