code: def from_callback(
      cls,
      callback,
      batch=False,
      prefetch_queue_depth=1,
      bytes_per_sample_hint=None,
  ):
      _, source_desc = get_callback_from_source(callback, cycle=None)
      return cls(
          source_desc,
          batch,
          prefetch_queue_depth,
          bytes_per_sample_hint,
      )
  
imports: from nvidia.dali._multiproc.pool import WorkerPool
  from nvidia.dali._multiproc.messages import TaskArgs, SampleRange
  from contextlib import closing
  from nvidia.dali._utils.external_source_impl import get_callback_from_source
  from nvidia.dali.types import SampleInfo
  from functools import wraps
  import numpy
  import os
  from nose.tools import with_setup
  from nose_utils import raises
  from test_pool_utils import capture_processes, setup_function, teardown_function
label_desc: Use image node_id 2 for calling the MockGroup obj's underlying member method code with example usage: obj.from_callback(cls, callback, batch, prefetch_queue_depth, bytes_per_sample_hint) and returns: cls