code: def read_extra_lines(self, filename):
          
          data = np.atleast_2d(np.loadtxt(filename))
          for nr, coords in enumerate(data):
              p1 = [coords[0], coords[1]]
              p2 = [coords[2], coords[3]]
              index = self.add_line(p1, p2, self.char_lengths['extra_line'])
              self.ExtraLineIndices.append(index)
docs: Read extra lines from the given filename. Each line is defined in
          one line with four coordinates: x1 y1 x2 y2. (x1,y1) denotes the
          starting point, (x2, y2) the end point of the line.