code: def optimizer(self):
      lr = tf.get_variable(
          "learning_rate", initializer=0.1, trainable=False
      )
      opt = tf.train.MomentumOptimizer(lr, 0.9)
      return opt
  
file_path: tensorpack/examples/ResNet/cifar10-preact18-mixup.py
imports: import argparse
  import numpy
  import os
  from tensorpack import *
  from tensorpack.compat import tfv1
  from tensorpack.dataflow import dataset
  from tensorpack.tfutils.summary import *
label_desc: Use image node_id 3 for calling the ResNet_Cifar obj's underlying member method code with example usage: obj.optimizer() and returns: opt