How to use the visidata.ColumnItem function in visidata

from visidata import Sheet, ColumnItem, asyncthread, globalCommand, ENTER
import vgit


class GitGrep(vgit.GitSheet):
    rowtype = 'results' # rowdef: list(file, line, line_contents)
    columns = [
        ColumnItem('filename', 0),
        ColumnItem('linenum', 1),
        ColumnItem('line', 2),
    ]
    @asyncthread
    def reload(self):
        tmp = (self.topRowIndex, self.cursorRowIndex)
        self.rows = []
        for line in self.git_lines('grep', '--no-color', '-z', '--line-number', '--ignore-case', self.regex):
            self.addRow(line.split('\0'))
        self.topRowIndex, self.cursorRowIndex = tmp


Sheet.unbindkey('g/')
globalCommand('g/', 'git-grep', 'rex=input("git grep: "); vd.push(GitGrep(rex, regex=rex, source=sheet))', 'find in all files in this repo'),

GitGrep.addCommand(ENTER, 'dive-row', 'vs=GitFileSheet(cursorRow[0]); vs.cursorRowIndex=int(cursorRow[1])-1; vs.reload(); vd.push(vs)', 'go to this match')
GitGrep.addCommand('^O', 'sysopen-row', 'launchExternalEditorPath(Path(cursorRow[0]), linenum=cursorRow[1]); reload()', 'open this file in $EDITOR')

def reload_sync(self):
        'Perform synchronous loading of TSV file, discarding header lines.'
        header_lines = options.get('header', self)
        delim = options.get('delimiter', self)

        with self.source.open_text() as fp:
            # get one line anyway to determine number of columns
            lines = list(getlines(fp, int(header_lines) or 1))
            headers = [L.split(delim) for L in lines]

            if header_lines <= 0:
                self.columns = [ColumnItem('', i) for i in range(len(headers[0]))]
            else:
                self.columns = [
                    ColumnItem('\\n'.join(x), i)
                        for i, x in enumerate(zip(*headers[:header_lines]))
                    ]

            lines = lines[header_lines:]  # in case of header_lines == 0
            self._rowtype = namedlist('tsvobj', [c.name for c in self.columns])

            self.recalc()
            self.rows = []

            with Progress(total=self.source.filesize) as prog:
                for L in itertools.chain(lines, getlines(fp)):
                    row = L.split(delim)
                    ncols = self._rowtype.length()  # current number of cols

for i, x in enumerate(zip(*headers[:header_lines]))
                    ]

            lines = lines[header_lines:]  # in case of header_lines == 0
            self._rowtype = namedlist('tsvobj', [c.name for c in self.columns])

            self.recalc()
            self.rows = []

            with Progress(total=self.source.filesize) as prog:
                for L in itertools.chain(lines, getlines(fp)):
                    row = L.split(delim)
                    ncols = self._rowtype.length()  # current number of cols
                    if len(row) > ncols:
                        # add unnamed columns to the type not found in the header
                        newcols = [ColumnItem('', len(row)+i, width=8) for i in range(len(row)-ncols)]
                        self._rowtype = namedlist(self._rowtype.__name__, list(self._rowtype._fields) + ['_' for c in newcols])
                        for c in newcols:
                            self.addColumn(c)
                    elif len(row) < ncols:
                        # extend rows that are missing entries
                        row.extend([None]*(ncols-len(row)))

                    self.addRow(self._rowtype(row))
                    prog.addProgress(len(L))

from visidata import Sheet, ColumnItem, asyncthread, globalCommand, ENTER
import vgit


class GitGrep(vgit.GitSheet):
    rowtype = 'results' # rowdef: list(file, line, line_contents)
    columns = [
        ColumnItem('filename', 0),
        ColumnItem('linenum', 1),
        ColumnItem('line', 2),
    ]
    @asyncthread
    def reload(self):
        tmp = (self.topRowIndex, self.cursorRowIndex)
        self.rows = []
        for line in self.git_lines('grep', '--no-color', '-z', '--line-number', '--ignore-case', self.regex):
            self.addRow(line.split('\0'))
        self.topRowIndex, self.cursorRowIndex = tmp


Sheet.unbindkey('g/')
globalCommand('g/', 'git-grep', 'rex=input("git grep: "); vd.push(GitGrep(rex, regex=rex, source=sheet))', 'find in all files in this repo'),

GitGrep.addCommand(ENTER, 'dive-row', 'vs=GitFileSheet(cursorRow[0]); vs.cursorRowIndex=int(cursorRow[1])-1; vs.reload(); vd.push(vs)', 'go to this match')

statuslen = clipdraw(scr, vd.windowHeight-1, rightx, rstatus, attr, w=vs.windowWidth-1, rtl=True)
                rightx -= statuslen
                ret += statuslen
            except Exception as e:
                vd.exceptionCaught(e)

    if scr:
        curses.doupdate()
    return ret


class StatusSheet(Sheet):
    precious = False
    rowtype = 'statuses'  # rowdef: (priority, args, nrepeats)
    columns = [
        ColumnItem('priority', 0, type=int, width=0),
        ColumnItem('nrepeats', 2, type=int, width=0),
        ColumnItem('args', 1, width=0),
        Column('message', getter=lambda col,row: composeStatus(row[1], row[2])),
    ]
    colorizers = [
        RowColorizer(1, 'color_error', lambda s,c,r,v: r and r[0] == 3),
        RowColorizer(1, 'color_warning', lambda s,c,r,v: r and r[0] in [1,2]),
    ]

    def reload(self):
        self.rows = self.source

@VisiData.property
def statusHistorySheet(vd):
    return StatusSheet("status_history", source=vd.statusHistory[::-1])  # in reverse order

def addRow(self, row, index=None):
        super().addRow(row, index=index)
        if isinstance(row, dict):
            for k in row:
                if k not in self.colnames:
                    c = ColumnItem(k, type=deduceType(row[k]))
                    self.colnames[k] = c
                    self.addColumn(c)
            return row

def setCols(self, headerrows):
        self.columns = []
        for i, _ in enumerate(itertools.zip_longest(*headerrows)):
            self.addColumn(ColumnItem('', i))

        self.setColNames(headerrows)
        self._rowtype = namedlist('tsvobj', [(c.name or '_') for c in self.columns])

option('visibility', 0, 'visibility level (0=low, 1=high)')

def getOptionsSheet(sheet):
    optsheet = getattr(sheet, 'optionsSheet', None)
    if not optsheet:
        sheet.optionsSheet = OptionsSheet(sheet.name+"_options", source=sheet)

    return sheet.optionsSheet


class StatusSheet(Sheet):
    precious = False
    rowtype = 'statuses'  # rowdef: (priority, args, nrepeats)
    columns = [
        ColumnItem('priority', 0, type=int, width=0),
        ColumnItem('nrepeats', 2, type=int, width=0),
        ColumnItem('args', 1, width=0),
        Column('message', getter=lambda col,row: composeStatus(row[1], row[2])),
    ]
    colorizers = [
        RowColorizer(1, 'color_error', lambda s,c,r,v: r and r[0] == 3),
        RowColorizer(1, 'color_warning', lambda s,c,r,v: r and r[0] in [1,2]),
    ]

    def reload(self):
        self.rows = vd.statusHistory[::-1]


class ColumnsSheet(Sheet):
    rowtype = 'columns'
    _rowtype = Column
    _coltype = ColumnAttr

def reload(self):
        sheets = self.sources

        # first item in joined row is the key tuple from the first sheet.
        # first columns are the key columns from the first sheet, using its row (0)
        self.columns = []
        for i, c in enumerate(sheets[0].keyCols):
            self.addColumn(SubrowColumn(c.name, ColumnItem(c.name, i, type=c.type, width=c.width), 0))
        self.setKeys(self.columns)

        for sheetnum, vs in enumerate(sheets):
            # subsequent elements are the rows from each source, in order of the source sheets
            ctr = collections.Counter(c.name for c in vs.nonKeyVisibleCols)
            for c in vs.nonKeyVisibleCols:
                newname = c.name if ctr[c.name] == 1 else '%s_%s' % (vs.name, c.name)
                self.addColumn(SubrowColumn(newname, c, sheetnum+1))

        rowsBySheetKey = {}
        rowsByKey = {}

        groupRowsByKey(sheets, rowsBySheetKey, rowsByKey)

        self.rows = []