class_docstr: Base class for image-to-text problems.
class_docstr_tok: ["Base","class","for","image-to-text","problems","."]
code: def vocab_problem(self):
      raise NotImplementedError()
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import io
  import os
  import numpy
  from tensor2tensor.data_generators import generator_utils
  from tensor2tensor.data_generators import problem
  from tensor2tensor.data_generators import text_encoder
  from tensor2tensor.layers import common_layers
  from tensor2tensor.layers import modalities
  from tensor2tensor.utils import contrib
  from tensor2tensor.utils import metrics
  import tensorflow.compat.v1
label_desc: Use image node_id 2 for calling the Image2TextProblem obj's underlying member method code with example usage: obj.vocab_problem() without return types