code: def create_dataset(
              self, group, chunk_size, compression=None, compression_opts=None):
          
          group.attrs['format'] = self.dformat
          super(Features, self)._create_dataset(
              group, chunk_size, compression, compression_opts)
  
          # TODO attribute declared outside __init__ is not safe. Used
          # because Labels.create_dataset need it.
          if chunk_size != 'auto':
              self.nb_per_chunk = nb_per_chunk(
                  self.dtype.itemsize, self.dim, chunk_size)
          else:
              self.nb_per_chunk = 'auto'
docs: Initialize the features subgoup