code: def testExtractPolyphonicSequences(self):
      testing_lib.add_track_to_sequence(
          self.note_sequence, 0, [(60, 100, 0.0, 4.0)]
      )
      quantized_sequence = sequences_lib.quantize_note_sequence(
          self.note_sequence, steps_per_quarter=1
      )
  
      seqs, _ = polyphony_lib.extract_polyphonic_sequences(
          quantized_sequence
      )
      self.assertEqual(1, len(seqs))
  
      seqs, _ = polyphony_lib.extract_polyphonic_sequences(
          quantized_sequence, min_steps_discard=2, max_steps_discard=5
      )
      self.assertEqual(1, len(seqs))
  
      self.note_sequence.notes[0].end_time = 1.0
      self.note_sequence.total_time = 1.0
      quantized_sequence = sequences_lib.quantize_note_sequence(
          self.note_sequence, steps_per_quarter=1
      )
      seqs, _ = polyphony_lib.extract_polyphonic_sequences(
          quantized_sequence, min_steps_discard=3, max_steps_discard=5
      )
      self.assertEqual(0, len(seqs))
  
      self.note_sequence.notes[0].end_time = 10.0
      self.note_sequence.total_time = 10.0
      quantized_sequence = sequences_lib.quantize_note_sequence(
          self.note_sequence, steps_per_quarter=1
      )
      seqs, _ = polyphony_lib.extract_polyphonic_sequences(
          quantized_sequence, min_steps_discard=3, max_steps_discard=5
      )
      self.assertEqual(0, len(seqs))
  
imports: import copy
  from magenta.common import testing_lib
  from magenta.models.polyphony_rnn import polyphony_lib
  from note_seq import sequences_lib
  from note_seq import testing_lib
  from note_seq.protobuf import music_pb2
  import tensorflow.compat.v1
label_desc: Use image node_id 20 for calling the PolyphonyLibTest obj's underlying member method code with example usage: obj.testExtractPolyphonicSequences() without return types