text: #!/usr/bin/env python3
  
  # Copyright (c) Facebook, Inc. and its affiliates.
  # This source code is licensed under the MIT license found in the
  # LICENSE file in the root directory of this source tree.
  
  from parlai.core.teachers import FbDeprecatedDialogTeacher
  from .build import build
  
  import copy
  import os
  
  
  def _path(opt):
      build(opt)
      dt = opt['datatype'].split(':')[0]
      if dt == 'train':
          suffix = 'train.14M+.txt'
      elif dt == 'valid':
          suffix = 'validation_NECN.20k.txt'
      else:
          suffix = 'test_CN.10k.txt'
      return os.path.join(opt['datapath'], 'BookTest', 'booktest-gut', suffix)
  
  
  class DefaultTeacher(FbDeprecatedDialogTeacher):
      def __init__(self, opt, shared=None):
          opt = copy.deepcopy(opt)
          opt['datafile'] = _path(opt)
          if 'stream' not in opt['datatype']:
              print(
                  'Dataset might not fit in memory. If this is the case, use'
                  + ' streaming by setting "-dt '
                  + opt['datatype']
                  + ':stream".'
              )
          super().__init__(opt, shared)
  