Deterministically combine more than one source of entropy
Set $r = r_1 + r_2 - \mathsf{floor}(r_1 + r_2)$. One (possible) advantage of this approach is that the result will be uniformly random in [0, 1] even if only one of $r_1$, $r_2$ is uniformly random. (Assuming the two values are independent.)

In Python you can also express this as

r = (r1 + r2) % 1.0