def create_new_column_with_difference_between_2(df, column1, column2):
    """
    Return df with new delta column: column1 - column2

    Parameters
    ----------
    df: Pandas dataframe
    column1: Column string
    column2: Column string

    Returns
    -------
    Df with added delta column

    """

    df['delta_' + column1 + "_" + column2] = df[column1] - df[column2]

    return df