cumulative weights in random.choices
The total weight is 10+5+30+5=50.
Suppose the population is [1,2,3,4].
It returns 1 with probability 10/50 = 0.2
It returns 2 with probability 5/50 = 0.1
It returns 3 with probability 30/50 = 0.6
It returns 4 with probability 5/50 = 0.1