Train a TF graph.
  This function is deprecated. Prefer cleverhans.train.train when possible.
  cleverhans.train.train supports multiple GPUs but this function is still
  needed to support legacy models that do not support calling fprop more
  than once.

  :param sess: TF session to use when training the graph
  :param loss: tensor, the model training loss.
  :param x: input placeholder
  :param y: output placeholder (for labels)
  :param X_train: numpy array with training inputs
  :param Y_train: numpy array with training outputs
  :param save: boolean controlling the save operation
  :param init_all: (boolean) If set to true, all TF variables in the session
                   are (re)initialized, otherwise only previously
                   uninitialized variables are initialized before training.
  :param evaluate: function that is run after each training iteration
                   (typically to display the test/validation accuracy).
  :param feed: An optional dictionary that is appended to the feeding
               dictionary before the session runs. Can be used to feed
               the learning phase of a Keras model for instance.
  :param args: dict or argparse `Namespace` object.
               Should contain `nb_epochs`, `learning_rate`,
               `batch_size`
               If save is True, should also contain 'train_dir'
               and 'filename'
  :param rng: Instance of numpy.random.RandomState
  :param var_list: Optional list of parameters to train.
  :param fprop_args: dict, extra arguments to pass to fprop (loss and model).
  :param optimizer: Optimizer to be used for training
  :return: True if model trained

def train(sess, loss, x, y, X_train, Y_train, save=False,
          init_all=False, evaluate=None, feed=None, args=None,
          rng=None, var_list=None, fprop_args=None, optimizer=None):
  """
  Train a TF graph.
  This function is deprecated. Prefer cleverhans.train.train when possible.
  cleverhans.train.train supports multiple GPUs but this function is still
  needed to support legacy models that do not support calling fprop more
  than once.

  :param sess: TF session to use when training the graph
  :param loss: tensor, the model training loss.
  :param x: input placeholder
  :param y: output placeholder (for labels)
  :param X_train: numpy array with training inputs
  :param Y_train: numpy array with training outputs
  :param save: boolean controlling the save operation
  :param init_all: (boolean) If set to true, all TF variables in the session
                   are (re)initialized, otherwise only previously
                   uninitialized variables are initialized before training.
  :param evaluate: function that is run after each training iteration
                   (typically to display the test/validation accuracy).
  :param feed: An optional dictionary that is appended to the feeding
               dictionary before the session runs. Can be used to feed
               the learning phase of a Keras model for instance.
  :param args: dict or argparse `Namespace` object.
               Should contain `nb_epochs`, `learning_rate`,
               `batch_size`
               If save is True, should also contain 'train_dir'
               and 'filename'
  :param rng: Instance of numpy.random.RandomState
  :param var_list: Optional list of parameters to train.
  :param fprop_args: dict, extra arguments to pass to fprop (loss and model).
  :param optimizer: Optimizer to be used for training
  :return: True if model trained
  """
  warnings.warn("This function is deprecated and will be removed on or after"
                " 2019-04-05. Switch to cleverhans.train.train.")

  args = _ArgsWrapper(args or {})
  fprop_args = fprop_args or {}

  # Check that necessary arguments were given (see doc above)
  assert args.nb_epochs, "Number of epochs was not given in args dict"
  if optimizer is None:
    assert args.learning_rate is not None, ("Learning rate was not given "
                                            "in args dict")
  assert args.batch_size, "Batch size was not given in args dict"

  if save:
    assert args.train_dir, "Directory for save was not given in args dict"
    assert args.filename, "Filename for save was not given in args dict"

  if rng is None:
    rng = np.random.RandomState()

  # Define optimizer
  loss_value = loss.fprop(x, y, **fprop_args)
  if optimizer is None:
    optimizer = tf.train.AdamOptimizer(learning_rate=args.learning_rate)
  else:
    if not isinstance(optimizer, tf.train.Optimizer):
      raise ValueError("optimizer object must be from a child class of "
                       "tf.train.Optimizer")
  # Trigger update operations within the default graph (such as batch_norm).
  with tf.control_dependencies(tf.get_collection(tf.GraphKeys.UPDATE_OPS)):
    train_step = optimizer.minimize(loss_value, var_list=var_list)

  with sess.as_default():
    if hasattr(tf, "global_variables_initializer"):
      if init_all:
        tf.global_variables_initializer().run()
      else:
        initialize_uninitialized_global_variables(sess)
    else:
      warnings.warn("Update your copy of tensorflow; future versions of "
                    "CleverHans may drop support for this version.")
      sess.run(tf.initialize_all_variables())

    for epoch in xrange(args.nb_epochs):
      # Compute number of batches
      nb_batches = int(math.ceil(float(len(X_train)) / args.batch_size))
      assert nb_batches * args.batch_size >= len(X_train)

      # Indices to shuffle training set
      index_shuf = list(range(len(X_train)))
      rng.shuffle(index_shuf)

      prev = time.time()
      for batch in range(nb_batches):

        # Compute batch start and end indices
        start, end = batch_indices(
            batch, len(X_train), args.batch_size)

        # Perform one training step
        feed_dict = {x: X_train[index_shuf[start:end]],
                     y: Y_train[index_shuf[start:end]]}
        if feed is not None:
          feed_dict.update(feed)
        train_step.run(feed_dict=feed_dict)
      assert end >= len(X_train)  # Check that all examples were used
      cur = time.time()
      _logger.info("Epoch " + str(epoch) + " took " +
                   str(cur - prev) + " seconds")
      if evaluate is not None:
        evaluate()

    if save:
      save_path = os.path.join(args.train_dir, args.filename)
      saver = tf.train.Saver()
      saver.save(sess, save_path)
      _logger.info("Completed model training and saved at: " +
                   str(save_path))
    else:
      _logger.info("Completed model training.")

  return True