Apart from tk.TOP and tk.LEFT, you can pass the tk.BOTTOM and tk.RIGHT constants to the side option. They perform the opposite stacking, as their names suggest; however, it may be counterintuitive since the natural order we follow is from top to bottom and from left to right.

For instance, if we replace the tk.LEFT value with tk.RIGHT in our three last widgets, their order from left to right would be label_e, label_d, and label_c.