cumulative weights in random.choices

Question

I am confused using the new random.choices in Python 3.6.

Here is the doc :

 random.choices(population, weights=None, *, cum_weights=None, k=1) 

-- Return a k sized list of elements chosen from the population with replacement. If the population is empty, raises IndexError .

They give an example: weights=[10, 5, 30, 5] and I don't know what this means. Why don't they sum to 100? If my population is [1, 2, 3, 4] -- does this mean that a choice of '10' occurs with probability 0.1?

Answer 1

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