'Step 1: define the placeholders for input and output'

def _create_placeholders(self):

    with tf.name_scope('data'):
        self.center_words = tf.placeholder(tf.int32, shape=[self.batch_size], name='center_words')
        self.target_words = tf.placeholder(tf.int32, shape=[self.batch_size, 1], name='target_words')
