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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 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])