code: def _copy_extra_fields(boxlist_to_copy_to, boxlist_to_copy_from):
      """Copies the extra fields of boxlist_to_copy_from to boxlist_to_copy_to.
  
      Args:
        boxlist_to_copy_to: BoxList to which extra fields are copied.
        boxlist_to_copy_from: BoxList from which fields are copied.
  
      Returns:
        boxlist_to_copy_to with extra fields.
      """
      for field in boxlist_to_copy_from.get_extra_fields():
          boxlist_to_copy_to.add_field(
              field, boxlist_to_copy_from.get_field(field)
          )
      return boxlist_to_copy_to
  
file_path: DALI/docs/examples/use_cases/tensorflow/efficientdet/pipeline/tf/preprocessor.py
imports: import tensorflow.compat.v1
  from pipeline.anchors_utils import box_list
label_desc: Use image node_id 8 for calling a global function with example usage: _copy_extra_fields(boxlist_to_copy_to, boxlist_to_copy_from) and returns: boxlist_to_copy_to