code: def compute_codec(self):
      codec = set()
      for text in self.text:
          codec = codec.union(set(text))
  
      return list(codec)
  
file_path: calamari/calamari_ocr/ocr/dataset/datareader/hdf5/hdf5_dataset_writer.py
imports: import numpy
  import h5py
  from tfaip import PipelineMode
label_desc: Use image node_id 4 for calling the Hdf5DatasetWriter obj's underlying member method code with example usage: obj.compute_codec() and returns: list