def convert_to_iris(dict_):
    """Change all appearances of ``short_name`` to ``var_name``.

    Parameters
    ----------
    dict_ : dict
        Dictionary to convert.

    Returns
    -------
    dict
        Converted dictionary.

    Raises
    ------
    KeyError
        :obj:`dict` contains keys``'short_name'`` **and** ``'var_name'``.

    """
    dict_ = dict(dict_)
    if 'short_name' in dict_:
        if 'var_name' in dict_:
            raise KeyError(
                f"Cannot replace 'short_name' by 'var_name', dictionary "
                f"already contains 'var_name' (short_name = "
                f"'{dict_['short_name']}', var_name = '{dict_['var_name']}')")
        dict_['var_name'] = dict_.pop('short_name')
    return dict_