def select_dfg(structures, dfg_conformation):
    """
    Filter structures based on selected DFG conformation(s).

    Parameters
    ----------
    structures : pandas.DataFrame
        Structures DataFrame from opencadd.databases.klifs module.
    dfg_conformation : str of list of str
        DFG conformation(s).

    Returns
    -------
    pandas.DataFrame
        Filtered DataFrame.
    """
    if not isinstance(dfg_conformation, list):
        dfg_conformation = [dfg_conformation]
    return structures[structures["structure.dfg"].isin(dfg_conformation)]