# basic for loop def f(): for x in range(2): for y in range(2): for z in range(2): print(x, y, z) f() # range with negative step for i in range(3, -1, -1): print(i) a = -1 # range with non-constant step - we optimize constant steps, so this # will be executed differently for i in range(3, -1, a): print(i)