def flatten(self, df, column_name):
        """Flatten a column in the dataframe that contains lists"""
        _exp_list = [[md5, x] for md5, value_list in zip(df['md5'], df[column_name]) for x in value_list]
        return pd.DataFrame(_exp_list, columns=['md5',column_name])
Flatten a column in the dataframe that contains lists