def __replace_index(selfs, df, indexCol):
    """
        For internal use. If the user requests a certain column be the index, this function puts that column as the first in the data frame df
        """
    if indexCol in df.columns:
        df.set_index(indexCol, drop=True, inplace=True)
        df.reset_index(inplace=True)
    else:
        print('Warning: the column ' + '"' + indexCol +
            '" you requested as the index is not found and therefore not included in the output.'
            )
    return df
