How to multiply every NINTH element of a list by 2?

Question

Python

Hello! A question. How to multiply every ninth element of a list by 2?
Tried like this, it doesn't work. I don't understand, what is the correct syntax?
The array samples_null_listcontains floating point numbers.

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])

Answer 1

Your code probably solves some problem, but not exactly described by you.
See range(start, stop[, step]) :

• start -- first interval value
  
• stop -- the last value of the interval
  
• step -- step
  

for i in range(..) means for each i in the range from start to stop with step . You pass the values ​​of the samples_null_list array as start, stop and step , so the behavior of the loop depends on the values ​​of this array (namely the first, last and ninth element).

Answer 2

new_list = []
for i, x in enumerate(my_list):
    if (i+1) % 9 == 0:
        x *= 2
    new_list.append(x)

Answer 3

Use index access. And it will be for i in tange(list_length)...

Answer 4

>>> 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]
>>>