class_docstr: SGD with momentum.
code: def lr(self):
      return self._lr
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import functools
  import re
  import gin
  from mesh_tensorflow import layers
  from mesh_tensorflow import ops_with_redefined_builtins
  import tensorflow.compat.v1
label_desc: Use image node_id 2 for calling the MomentumOptimizer obj's underlying member method code with example usage: obj.lr() and returns: self