code: def define_graph(self):
      data = fn.external_source(lambda: next(self.iterator))
      out = data.gpu() if self.device == "gpu" else data
      if self.per_sample_coeff:
          preemph_coeff_arg = self.uniform()
          return self.preemph(out, preemph_coeff=preemph_coeff_arg)
      else:
          return self.preemph(out)
  
file_path: DALI/dali/test/python/operator_2/test_preemph.py
imports: from nvidia.dali.pipeline import Pipeline
  import nvidia.dali.ops
  import nvidia.dali.fn
  import numpy
  from functools import partial
  from test_utils import compare_pipelines
  from test_utils import RandomlyShapedDataIterator
label_desc: Use image node_id 2 for calling the PreemphasisPipeline obj's underlying member method code with example usage: obj.define_graph() and returns: self, self