docstr: Adds placeholders to graph.
docstr_tok: ["Adds","placeholders","to","graph","."]
code: def add_placeholders(self):
      """Adds placeholders to graph."""
      #################################################################### DEBUG
      # self.test_label_placeholder = Input(
      #    tensor=tf.placeholder(dtype='float32', shape=(self.test_batch_size),
      #    name="label_placeholder"))
      # self.test_weight_placeholder = Input(
      #    tensor=tf.placeholder(dtype='float32', shape=(self.test_batch_size),
      #    name="weight_placeholder"))
      self.test_label_placeholder = tf.placeholder(
          dtype="float32",
          shape=(self.test_batch_size),
          name="label_placeholder",
      )
      self.test_weight_placeholder = tf.placeholder(
          dtype="float32",
          shape=(self.test_batch_size),
          name="weight_placeholder",
      )
  
      # TODO(rbharath): Should weights for the support be used?
      # Support labels
      # self.support_label_placeholder = Input(
      #    tensor=tf.placeholder(dtype='float32', shape=[self.support_batch_size],
      #    name="support_label_placeholder"))
      self.support_label_placeholder = tf.placeholder(
          dtype="float32",
          shape=[self.support_batch_size],
          name="support_label_placeholder",
      )
      self.phase = tf.placeholder(
          dtype="bool", name="keras_learning_phase"
      )
  
imports: from __future__ import print_function
  from __future__ import division
  from __future__ import unicode_literals
  import warnings
  import numpy
  import tensorflow
  import sys
  import time
  from deepchem.models import Model
  from deepchem.data import pad_batch
  from deepchem.data import NumpyDataset
  from deepchem.metrics import to_one_hot
  from deepchem.metrics import from_one_hot
  from deepchem.models.tf_new_models.graph_topology import merge_dicts
  from deepchem.nn import model_ops
  from deepchem.data import SupportGenerator
  from deepchem.data import EpisodeGenerator
  from deepchem.data import get_task_dataset
  from deepchem.data import get_single_task_test
  from deepchem.data import get_task_dataset_minus_support
  from deepchem.nn.copy import Input
label_desc: Use image node_id 3 for calling the SupportGraphClassifier obj's underlying member method code with example usage: obj.add_placeholders() without return types