code: def optimizer(self):
      lr = tf.get_variable(
          "learning_rate", initializer=2e-4, trainable=False
      )
      return tf.train.AdamOptimizer(lr, beta1=0.5, epsilon=1e-3)
  
imports: import argparse
  import glob
  import os
  import tensorflow
  from six.moves import range
  from tensorpack import *
  from tensorpack.tfutils.scope_utils import auto_reuse_variable_scope
  from tensorpack.tfutils.summary import add_moving_summary
  from GAN import GANModelDesc, GANTrainer
label_desc: Use image node_id 6 for calling the Model obj's underlying member method code with example usage: obj.optimizer() and returns: tf