code: def _is_external_source(op_instance):
      return isinstance(op_instance._op, ExternalSource)
  
imports: from nvidia.dali import backend
  from nvidia.dali import tensors
  from nvidia.dali import types
  from nvidia.dali._multiproc.messages import TaskArgs, SampleRange
  import nvidia.dali.types
  from nvidia.dali._utils.external_source_impl import get_callback_from_source, accepted_arg_count, SourceKind
label_desc: Use image node_id 5 for calling a global function with example usage: _is_external_source(op_instance) and returns: isinstance