code: def flatten(cls, obj):
      for k in obj.keys():
          if not isinstance(k, str):
              raise KeyError(
                  "Only support flattening dictionaries if keys are str."
              )
      keys = sorted(obj.keys())
      values = [obj[k] for k in keys]
      ret, schema = ListSchema.flatten(values)
      return ret, cls(schema.schemas, schema.sizes, keys)
  
imports: import collections
  from dataclasses import dataclass
  from typing import Callable, List, Optional, Tuple
  import torch
  from torch import nn
  from detectron2.structures import Boxes, Instances, ROIMasks
  from detectron2.utils.registry import _convert_target_to_string, locate
  from .torchscript_patch import patch_builtin_len
label_desc: Use image node_id 2 for calling the DictSchema obj's underlying member method code with example usage: obj.flatten(cls, obj) and returns: ret,  cls