code: def get_mode(orig_string):
      if orig_string is None:
          string = config.mode
      else:
          string = orig_string
      if not isinstance(string, str):
          return string  # it is hopefully already a mode...
  
      global instantiated_default_mode
      # The default mode is cached. However, config.mode can change
      # If instantiated_default_mode has the right class, use it.
      if orig_string is None and instantiated_default_mode:
          if string in predefined_modes:
              default_mode_class = predefined_modes[
                  string
              ].__class__.__name__
          else:
              default_mode_class = string
          if (
              instantiated_default_mode.__class__.__name__
              == default_mode_class
          ):
              return instantiated_default_mode
  
      if string in ("Mode", "DebugMode", "NanGuardMode"):
          if string == "DebugMode":
              # need to import later to break circular dependency.
              from .debugmode import DebugMode
  
              # DebugMode use its own linker.
              ret = DebugMode(optimizer=config.optimizer)
          elif string == "NanGuardMode":
              # need to import later to break circular dependency.
              from .nanguardmode import NanGuardMode
  
              # NanGuardMode use its own linker.
              ret = NanGuardMode(
                  True, True, True, optimizer=config.optimizer
              )
          else:
              # TODO: Can't we look up the name and invoke it rather than using eval here?
              ret = eval(
                  string
                  + "(linker=config.linker, optimizer=config.optimizer)"
              )
      elif string in predefined_modes:
          ret = predefined_modes[string]
      else:
          raise Exception(
              f"No predefined mode exist for string: {string}"
          )
  
      if orig_string is None:
          # Build and cache the default mode
          if config.optimizer_excluding:
              ret = ret.excluding(
                  *config.optimizer_excluding.split(":")
              )
          if config.optimizer_including:
              ret = ret.including(
                  *config.optimizer_including.split(":")
              )
          if config.optimizer_requiring:
              ret = ret.requiring(
                  *config.optimizer_requiring.split(":")
              )
          instantiated_default_mode = ret
  
      return ret
  
imports: import logging
  import warnings
  from typing import Literal, Optional, Union
  from pytensor.compile.function.types import Supervisor
  from pytensor.configdefaults import config
  from pytensor.graph.destroyhandler import DestroyHandler
  from pytensor.graph.rewriting.basic import CheckStackTraceRewriter, GraphRewriter, MergeOptimizer, NodeProcessingGraphRewriter
  from pytensor.graph.rewriting.db import EquilibriumDB, LocalGroupDB, RewriteDatabase, RewriteDatabaseQuery, SequenceDB, TopoDB
  from pytensor.link.basic import Linker, PerformLinker
  from pytensor.link.c.basic import CLinker, OpWiseCLinker
  from pytensor.link.jax.linker import JAXLinker
  from pytensor.link.numba.linker import NumbaLinker
  from pytensor.link.vm import VMLinker
label_desc: Use image node_id 3 for calling a global function with example usage: get_mode(orig_string) and returns: ret, string, instantiated_default_mode