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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 combine_expression_columns(df, columns_to_combine, remove_combined=True):
 """ Combine expression columns, calculating the mean for 2 columns :param df: Pandas dataframe :param columns_to_combine: A list of tuples containing the column names to combine :return: """


    df = df.copy()

    for ca, cb in columns_to_combine:
        df["%s_(x+y)/2_%s" % (ca, cb)] = (df[ca] + df[cb]) / 2

    if remove_combined:
        for ca, cb in columns_to_combine:
            df.drop([ca, cb], inplace=True, axis=1)

    return df