class_docstr: This layer aims to build a mapping from raw keys to indices within [0, max_index).
  The mapping is continuously built during training. The mapping will be frozen during
  evaluation and prediction. Unseen keys will be assigned to index 0.
code: def add_eval_ops(self, net):
      net.IndexFreeze(self.handler, self.handler)
      self.add_train_ops(net)
  
file_path: pytorch/caffe2/python/layers/build_index.py
imports: import numpy
  from caffe2.python import core, schema
  from caffe2.python.layers.layers import ModelLayer
label_desc: Use image node_id 3 for calling the MapToRange obj's underlying member method code with example usage: obj.add_eval_ops(net) without return types