Multiply every other element in a list

Question

I have a list, let\'s say: list = [6,2,6,2,6,2,6], and I want it to create a new list with every other element multiplied by 2 and every other element multiplie

Answer 1

You can use slice assignment and list comprehension:

l = oldlist[:]
l[::2] = [x*2 for x in l[::2]]

Your solution is wrong because:

1. The function doesn't take any arguments
2. res is declared as a number and not a list
3. Your loop has no way of knowing the index
4. You return on the first loop iteration
5. Not related to the function, but you didn't actually call multi

Here's your code, corrected:

def multi(lst):
    res = list(lst) # Copy the list
    # Iterate through the indexes instead of the elements
    for i in range(len(res)):
        if i % 2 == 0:
            res[i] = res[i]*2 
    return res

print(multi([12,2,12,2,12,2,12]))