code: def lookup_backend(compiler_fn):
      """Expand backend strings to functions"""
      if isinstance(compiler_fn, str):
          if compiler_fn not in _BACKENDS:
              _lazy_import()
          if compiler_fn not in _BACKENDS:
              _lazy_import_entry_point(compiler_fn)
          if compiler_fn not in _BACKENDS:
              from ..exc import InvalidBackend
  
              raise InvalidBackend(name=compiler_fn)
          compiler_fn = _BACKENDS[compiler_fn]
      return compiler_fn
  
file_path: pytorch/torch/_dynamo/backends/registry.py
imports: import functools
  import sys
  from typing import Callable, Dict, List, Optional, Protocol, Sequence, Tuple
  import torch
  from torch import fx
label_desc: Use image node_id 2 for calling a global function with example usage: lookup_backend(compiler_fn) and returns: compiler_fn