docs: def _read_group_h5(filename, groupname):
      """Return group content.
  
      Args:
          filename (:class:`pathlib.Path`): path of hdf5 file.
          groupname (str): name of group to read.
      Returns:
          :class:`numpy.array`: content of group.
      """
      with h5py.File(filename, 'r') as h5f:
          data = h5f[groupname][()]
      return data