code: def add_columns(self):
      for i in range(self.num_cols):
          column = Gtk.TreeViewColumn(
              str(i), Gtk.CellRendererText(), text=i
          )
          self.treeview.append_column(column)
  
file_path: matplotlib/galleries/examples/user_interfaces/gtk4_spreadsheet_sgskip.py
imports: import gi
  from gi.repository import Gtk
  from numpy.random import random
  from matplotlib.backends.backend_gtk4agg import FigureCanvas
  from matplotlib.figure import Figure
label_desc: Use image node_id 3 for calling the DataManager obj's underlying member method code with example usage: obj.add_columns() without return types