Return a tuple of sections and section titles.
    Sections are pretty print of model coefficients

    Parameters
    ----------
    top_coefs : SFrame of top k coefficients

    bottom_coefs : SFrame of bottom k coefficients

    Returns
    -------
    (sections, section_titles) : tuple
            sections : list
                summary sections for top/bottom k coefficients
            section_titles : list
                summary section titles

def _summarize_coefficients(top_coefs, bottom_coefs):
    """
    Return a tuple of sections and section titles.
    Sections are pretty print of model coefficients

    Parameters
    ----------
    top_coefs : SFrame of top k coefficients

    bottom_coefs : SFrame of bottom k coefficients

    Returns
    -------
    (sections, section_titles) : tuple
            sections : list
                summary sections for top/bottom k coefficients
            section_titles : list
                summary section titles
    """

    def get_row_name(row):
        if row['index'] is None:
            return row['name']
        else:
            return "%s[%s]" % (row['name'], row['index'])

    if len(top_coefs) == 0:
        top_coefs_list = [('No Positive Coefficients', _precomputed_field('') )]
    else:
        top_coefs_list = [ (get_row_name(row),
                            _precomputed_field(row['value'])) \
                            for row in top_coefs ]

    if len(bottom_coefs) == 0:
        bottom_coefs_list = [('No Negative Coefficients', _precomputed_field(''))]
    else:
        bottom_coefs_list = [ (get_row_name(row),
                            _precomputed_field(row['value'])) \
                            for row in bottom_coefs ]

    return ([top_coefs_list, bottom_coefs_list], \
                    [ 'Highest Positive Coefficients', 'Lowest Negative Coefficients'] )