code: def __getitem__(self, x, nn=None):
      try:
          return self.cache[x]
      except KeyError:
          self.index += 1
          xval = self.Vertex(x, index=self.index)
          # logging.info("New generated vertex at x = {}".format(x))
          # NOTE: Surprisingly high performance increase if logging
          # is commented out
          self.cache[x] = xval
          return self.cache[x]
  
imports: import collections
  from abc import ABC, abstractmethod
  import numpy
  from scipy._lib._util import MapWrapper
label_desc: Use image node_id 2 for calling the VertexCacheIndex obj's underlying member method code with example usage: obj.__getitem__(x, nn) and returns: self, self