code: def train_op(x, label):
      g, v = gv(x, label)  # returns gradients, loss
      opt(lr, g)
      return v
  
file_path: objax/examples/image_classification/horses_or_humans_logistic.py
imports: import os
  import numpy
  import tensorflow_datasets
  import objax
  from objax.util import EasyDict
label_desc: Use image node_id 3 for calling a global function with example usage: train_op(x, label) and returns: v