Rotating values in a list [Python]

I understand this question has been asked before but I haven't seen any that answer it in a way without splitting the list.

say I have a list:

num = [1,2,3,4,5,6]

I want to create a function:

rotate(lst, x):

So that if I call rotate(num, 3) it will globally edit the list num. That way when I later call print(num) it will result in [4,5,6,1,2,3].

I understand that I could write the function something like:

rotate(lst, x):
    return [lst[-x:] + lst[:-x]

But I need to do this function without a return statement, and without splitting the list. What I'm thinking would work would be to put the last value of the list into a variable: q = lst[-1] and then from there create a loop that runs x amount of times that continues to move the values towards the end of the list and replacing the 0th position with whatever is stored in q.

One more thing. If I call rotate(lst, -3) then instead of rotating to the "right" it would have to rotate to the "left".

I'm new to python and having trouble wrapping my mind around this concept of manipulating lists. Thank you everyone for your time and effort. I hope this problem was clear enough.

Try:

num = [1,2,3,4,5,6]

def rotate(lst,x):
    copy = list(lst)
    for i in range(len(lst)):
        if x<0:
            lst[i+x] = copy[i]
        else:
            lst[i] = copy[i-x]

rotate(num, 2)

print num