code: def save(self, filename):
      faiss.write_index(self.index, filename)
  
imports: import numpy
  import torch
  from ..distances import BatchedDistance, CosineSimilarity
  from .None import common_functions
label_desc: Use image node_id 5 for calling the FaissKNN obj's underlying member method code with example usage: obj.save(filename) without return types