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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 get_sigma(database_file_name='', e_min=np.NaN, e_max=np.NaN, e_step=np.NaN, t_kelvin=None):
 """retrieve the Energy and sigma axis for the given isotope :param database_file_name: path/to/file with extension :type database_file_name: string :param e_min: left energy range in eV of new interpolated data :type e_min: float :param e_max: right energy range in eV of new interpolated data :type e_max: float :param e_step: energy step in eV for interpolation :type e_step: float :param t_kelvin: temperature in Kelvin :type t_kelvin: float :return: {'energy': np.array, 'sigma': np.array} :rtype: dict """


    file_extension = os.path.splitext(database_file_name)[1]

    if t_kelvin is None:
        # '.csv' files
        if file_extension != '.csv':
            raise IOError("Cross-section File type must be '.csv'")
        else:
            _df = get_database_data(file_name=database_file_name)
            _dict = get_interpolated_data(df=_df, e_min=e_min, e_max=e_max,
                                          e_step=e_step)
            return {'energy_eV': _dict['x_axis'],
                    'sigma_b': _dict['y_axis']}
    else:
        raise ValueError("Doppler broadened cross-section in not yet supported in current version.")