def _update_index_on_df(df, index_names):
    """Helper function to restore index information after collection. Doesn't
    use self so we can serialize this."""
    if index_names:
        df = df.set_index(index_names)
        # Remove names from unnamed indexes
        index_names = _denormalize_index_names(index_names)
        df.index.names = index_names
    return df
Helper function to restore index information after collection. Doesn't
    use self so we can serialize this.