'Builds the ops for reading input data.
Outputs:
self.encode_ids
self.decode_pre_ids
self.decode_post_ids
self.encode_mask
self.decode_pre_mask
self.decode_post_mask'

def build_inputs(self):

    if (self.mode == 'encode'):
        encode_ids = None
        decode_pre_ids = None
        decode_post_ids = None
        encode_mask = tf.placeholder(tf.int8, (None, None), name='encode_mask')
        decode_pre_mask = None
        decode_post_mask = None
    else:
        input_queue = input_ops.prefetch_input_data(self.reader, self.config.input_file_pattern, shuffle=self.config.shuffle_input_data, capacity=self.config.input_queue_capacity, num_reader_threads=self.config.num_input_reader_threads)
        serialized = input_queue.dequeue_many(self.config.batch_size)
        (encode, decode_pre, decode_post) = input_ops.parse_example_batch(serialized)
        encode_ids = encode.ids
        decode_pre_ids = decode_pre.ids
        decode_post_ids = decode_post.ids
        encode_mask = encode.mask
        decode_pre_mask = decode_pre.mask
        decode_post_mask = decode_post.mask
    self.encode_ids = encode_ids
    self.decode_pre_ids = decode_pre_ids
    self.decode_post_ids = decode_post_ids
    self.encode_mask = encode_mask
    self.decode_pre_mask = decode_pre_mask
    self.decode_post_mask = decode_post_mask
