code: def __call__(self, sample_info):
      a = super().__call__(sample_info)
      return mx.nd.array(a, dtype=a.dtype)
  
file_path: DALI/dali/test/python/test_external_source_parallel_mxnet.py
imports: import mxnet
  from nose import with_setup
  from nose_utils import raises
  from test_pool_utils import setup_function
  from test_external_source_parallel_utils import ExtCallback, check_spawn_with_callback, create_pipe, build_and_run_pipeline
  import numpy
label_desc: Use image node_id 1 for calling the ExtCallbackMX obj's underlying member method code with example usage: obj.__call__(sample_info) and returns: mx