def data_description(hf, var):
    """data_description(hf, var)

    Returns the description of an output variable. If the
    description is empty, returns the variable name.

    Args:
      hf: An open HDF5 filehandle or a string containing the HDF5
        filename to use.
      var: Output variable name.
    """
    desc = hf['/output/data/%s' % var].attrs['description']
    if type(desc) != str:
        desc = desc.decode('UTF-8')

    if desc:
        return desc
    return var