code: def test_4bit(self):
      self.do_test(32, 4, nbit=4)
  
imports: from __future__ import absolute_import, division, print_function
  import numpy
  import faiss
  import unittest
label_desc: Use image node_id 7 for calling the TestPQTables obj's underlying member method code with example usage: obj.test_4bit() without return types