Works in 3.6+
random.choices([1,2], weights=[0.001, 0.8], k=1)[0]
Here is proof that makes 100k choices from [1,2] array and then counts numbers:
arr = [ch[0] for ch in [random.choices([1,2], weights=[0.001, 0.8], k=1) for _ in range(100000)]]
>>> arr.count(1), arr.count(2)
(114, 99886)
