code: def loss(self, a, p, n):
      return triplet_loss(a, p, n, 5.0, extra=True, scope="loss")
  
imports: import argparse
  import numpy
  import tensorflow
  import tensorflow.contrib.slim
  from tensorpack import *
  from tensorpack.tfutils.summary import add_moving_summary
  from tensorpack.utils.gpu import change_gpu
  from embedding_data import MnistPairs, MnistTriplets, get_test_data
label_desc: Use image node_id 3 for calling the TripletModel obj's underlying member method code with example usage: obj.loss(a, p, n) and returns: triplet_loss