code: def create_hdf_file(self):
          
          mode = 'w'
          if not self._overwrite and os.path.exists(self._fname):
              mode = 'a'
  
          self._hdf_file = h5py.File(self._fname, mode)
  
          if self._hdf_basepath == '/':
              self._group = self._hdf_file['/']
          else:
              self._group = self._hdf_file.create_group(self._hdf_basepath)
docs: :return: h5py DataSet