def _update(self, frame_no):
        if frame_no % 2 == 0:
            return

        y = self._y
        image, colours = self._renderer.rendered_text
        for i, line in enumerate(image):
            if self._screen.is_visible(0, y):
                x = (len(line) - self._screen.width) // 2
                for j, c in enumerate(line):
                    if c != " " and random() > 0.85:
                        if colours[i][j][0] is not None:
                            self._screen.print_at(c, x, y,
                                                  colours[i][j][0],
                                                  colours[i][j][1])
                        else:
                            self._screen.print_at(c, x, y, self._colour)
                    x += 1
            y += 1
dataset/ETHPy150Open peterbrittain/asciimatics/asciimatics/effects.py/Mirage._update/swapped operands of `-`