samples_null_list
записаны числа с плавающей точкой.step_null_list = []
for i in range(samples_null_list[0], samples_null_list[-1], samples_null_list[8]):
samples_list[i] *= 2
step_null_list.append(samples_list[i])
>>> lst = [1, 2, 3, 4, 5] * 10
>>>
>>> out = [n * 2 if i % 9 == 0 else n
... for i, n in enumerate(lst, 1)]
>>> out
[1, 2, 3, 4, 5, 1, 2, 3, 8, 5, 1, 2, 3, 4, 5, 1, 2, 6, 4, 5, 1, 2, 3, 4, 5, 1, 4, 3, 4, 5, 1, 2, 3, 4, 5, 2, 2, 3, 4, 5, 1, 2, 3, 4, 10, 1, 2, 3, 4, 5]
>>>