class_docstr: Track side effects (list mutation, setattr, etc) that need to be
  applied after an FX graph is run.
class_docstr_tok: ["Track","side","effects","(","list","mutation",",","setattr",",","etc",")","that","need","to","be","applied","after","an","FX","graph","is","run","."]
docstr: Start tracking a new variable for mutation
docstr_tok: ["Start","tracking","a","new","variable","for","mutation"]
code: def _track_obj(
      self,
      item: Any,
      variable: VariableTracker,
      mutable_cls=MutableSideEffects,
  ):
      """Start tracking a new variable for mutation"""
      assert variable.source is not None
      variable.mutable_local = mutable_cls(variable.source)
      self.id_to_variable[id(item)] = variable
      self.keepalive.append(item)
      return variable
  
imports: import inspect
  from typing import Any, Dict, List, Optional, Union
  import torch.nn
  from .None import utils, variables
  from .bytecode_transformation import create_call_function, create_call_method, create_instruction
  from .codegen import PyCodegen
  from .exc import unimplemented
  from .source import LocalSource, Source
  from .utils import nn_module_new, object_new
  from .variables.base import is_side_effect_safe, MutableLocalBase, MutableLocalSource, VariableTracker
label_desc: Use image node_id 19 for calling the SideEffects obj's underlying member method code with example usage: obj._track_obj(item, variable, mutable_cls) and returns: variable