class_docstr: Step with a standard implementation of input handling.
  
  Args:
    dataset_fn: a function that returns a tf.data Dataset that produces the
      input for the model.
code: def initialize(self):
      return self._iterator.initializer
  
file_path: tensorflow/tensorflow/python/distribute/step_fn.py
imports: from tensorflow.python.eager import backprop
  from tensorflow.python.training import optimizer
label_desc: Use image node_id 2 for calling the StandardInputStep obj's underlying member method code with example usage: obj.initialize() and returns: self