code: def evaluate_obj(self, centroids, x):
      index = faiss.IndexFlatL2(1)
      index.add(centroids)
      D, I = index.search(x, k=1)
      return D.sum()
  
imports: from __future__ import absolute_import, division, print_function
  import numpy
  import faiss
  import unittest
  import array
  from common_faiss_tests import get_dataset_2
label_desc: Use image node_id 1 for calling the TestClustering1D obj's underlying member method code with example usage: obj.evaluate_obj(centroids, x) and returns: D