docs: def show(self):
          """Show the data graphically in a new pop-up window."""
  
          # prevent the following error:
          # '_tkinter.TclError: no display name and no $DISPLAY environment
          #    variable'
          # import matplotlib
          # matplotlib.use('GTK3Agg', warn=False)
  
          import matplotlib.pyplot as plt
  
          pointlist = self.get_pointlist()
          if 'pen_down' in pointlist[0][0]:
              assert len(pointlist) > 1, \
                  "Lenght of pointlist was %i. Got: %s" % (len(pointlist),
                                                           pointlist)
              # Create a new pointlist that models pen-down strokes and pen
              # up strokes
              new_pointlist = []
              last_pendown_state = None
              stroke = []
              for point in pointlist[0]:
                  if last_pendown_state is None:
                      last_pendown_state = point['pen_down']
                  if point['pen_down'] != last_pendown_state:
                      new_pointlist.append(stroke)
                      last_pendown_state = point['pen_down']
                      stroke = []
                  else:
                      stroke.append(point)
              new_pointlist.append(stroke)  # add the last stroke
              pointlist = new_pointlist
  
          _, ax = plt.subplots()
          ax.set_title("Raw data id: %s, "
                       "Formula_id: %s" % (str(self.raw_data_id),
                                           str(self.formula_id)))
  
          colors = _get_colors(self.segmentation)
          for symbols, color in zip(self.segmentation, colors):
              for stroke_index in symbols:
                  stroke = pointlist[stroke_index]
                  xs, ys = [], []
                  for p in stroke:
                      xs.append(p['x'])
                      ys.append(p['y'])
                  if "pen_down" in stroke[0] and stroke[0]["pen_down"] is False:
                      plt.plot(xs, ys, '-x', color=color)
                  else:
                      plt.plot(xs, ys, '-o', color=color)
          plt.gca().invert_yaxis()
          ax.set_aspect('equal')
          plt.show()