How to use the birdears.urwid.util.calc_text_pos function in birdears

def _last_row(self, row):
        """On the last row we need to slide the bottom right character
        into place. Calculate the new line, attr and an insert sequence
        to do that.

        eg. last row:
        XXXXXXXXXXXXXXXXXXXXYZ

        Y will be drawn after Z, shifting Z into position.
        """

        new_row = row[:-1]
        z_attr, z_cs, last_text = row[-1]
        last_cols = util.calc_width(last_text, 0, len(last_text))
        last_offs, z_col = util.calc_text_pos(last_text, 0,
            len(last_text), last_cols-1)
        if last_offs == 0:
            z_text = last_text
            del new_row[-1]
            # we need another segment
            y_attr, y_cs, nlast_text = row[-2]
            nlast_cols = util.calc_width(nlast_text, 0,
                len(nlast_text))
            z_col += nlast_cols
            nlast_offs, y_col = util.calc_text_pos(nlast_text, 0,
                len(nlast_text), nlast_cols-1)
            y_text = nlast_text[nlast_offs:]
            if nlast_offs:
                new_row.append((y_attr, y_cs,
                    nlast_text[:nlast_offs]))
        else:

closest_pos = s
        s = closest_pos
        if s is None:
            return
        if s.end is None:
            return s.offs
        return calc_text_pos( text, s.offs, s.end, s.sc-1)[0]

    for seg in line_layout:
        s = LayoutSegment(seg)
        if s.offs is not None:
            if s.end is not None:
                if (current_sc <= pref_col and
                    pref_col < current_sc + s.sc):
                    # exact match within this segment
                    return calc_text_pos( text,
                        s.offs, s.end,
                        pref_col - current_sc )[0]
                elif current_sc <= pref_col:
                    closest_sc = current_sc + s.sc - 1
                    closest_pos = s

            if closest_sc is None or ( abs(pref_col-current_sc)
                    < abs(pref_col-closest_sc) ):
                # this screen column is closer
                closest_sc = current_sc
                closest_pos = s.offs
            if current_sc > closest_sc:
                # we're moving past
                break
        current_sc += s.sc

def code_span( s, fg, bg, cursor = -1):
    code_fg = _code_colours[ fg ]
    code_bg = _code_colours[ bg ]

    if cursor >= 0:
        c_off, _ign = util.calc_text_pos(s, 0, len(s), cursor)
        c2_off = util.move_next_char(s, c_off, len(s))

        return ( code_fg + code_bg + s[:c_off] + "\n" +
             code_bg + code_fg + s[c_off:c2_off] + "\n" +
             code_fg + code_bg + s[c2_off:] + "\n")
    else:
        return code_fg + code_bg + s + "\n"

if bg_r is None:
        bg_r, bg_g, bg_b = _d_bg_r, _d_bg_g, _d_bg_b
    html_fg = "#%02x%02x%02x" % (fg_r, fg_g, fg_b)
    html_bg = "#%02x%02x%02x" % (bg_r, bg_g, bg_b)
    if aspec.standout:
        html_fg, html_bg = html_bg, html_fg
    extra = (";text-decoration:underline" * aspec.underline +
        ";font-weight:bold" * aspec.bold)
    def html_span(fg, bg, s):
        if not s: return ""
        return ('<span style="color:%s;'
            'background:%s%s">%s</span>' %
            (fg, bg, extra, html_escape(s)))

    if cursor &gt;= 0:
        c_off, _ign = util.calc_text_pos(s, 0, len(s), cursor)
        c2_off = util.move_next_char(s, c_off, len(s))
        return (html_span(html_fg, html_bg, s[:c_off]) +
            html_span(html_bg, html_fg, s[c_off:c2_off]) +
            html_span(html_fg, html_bg, s[c2_off:]))
    else:
        return html_span(html_fg, html_bg, s)

y_attr, y_cs, nlast_text = row[-2]
            nlast_cols = util.calc_width(nlast_text, 0,
                len(nlast_text))
            z_col += nlast_cols
            nlast_offs, y_col = util.calc_text_pos(nlast_text, 0,
                len(nlast_text), nlast_cols-1)
            y_text = nlast_text[nlast_offs:]
            if nlast_offs:
                new_row.append((y_attr, y_cs,
                    nlast_text[:nlast_offs]))
        else:
            z_text = last_text[last_offs:]
            y_attr, y_cs = z_attr, z_cs
            nlast_cols = util.calc_width(last_text, 0,
                last_offs)
            nlast_offs, y_col = util.calc_text_pos(last_text, 0,
                last_offs, nlast_cols-1)
            y_text = last_text[nlast_offs:last_offs]
            if nlast_offs:
                new_row.append((y_attr, y_cs,
                    last_text[:nlast_offs]))

        new_row.append((z_attr, z_cs, z_text))
        return new_row, z_col-y_col, (y_attr, y_cs, y_text)

n_cr = len(text)
            sc = calc_width(text, p, n_cr)
            if sc == 0:
                # removed character hint
                b.append([(0,n_cr)])
                p = n_cr+1
                continue
            if sc <= width:
                # this segment fits
                b.append([(sc,p,n_cr),
                    # removed character hint
                    (0,n_cr)])

                p = n_cr+1
                continue
            pos, sc = calc_text_pos( text, p, n_cr, width )
            if pos == p: # pathological width=1 double-byte case
                raise CanNotDisplayText(
                    "Wide character will not fit in 1-column width")
            if wrap == 'any':
                b.append([(sc,p,pos)])
                p = pos
                continue
            assert wrap == 'space'
            if text[pos] == sp_o:
                # perfect space wrap
                b.append([(sc,p,pos),
                    # removed character hint
                    (0,pos)])
                p = pos+1
                continue
            if is_wide_char(text, pos):

if closest_sc is None or ( abs(pref_col-current_sc)
                    < abs(pref_col-closest_sc) ):
                # this screen column is closer
                closest_sc = current_sc
                closest_pos = s.offs
            if current_sc > closest_sc:
                # we're moving past
                break
        current_sc += s.sc

    if closest_pos is None or type(closest_pos) == int:
        return closest_pos

    # return the last positions in the segment "closest_pos"
    s = closest_pos
    return calc_text_pos( text, s.offs, s.end, s.sc-1)[0]