Python - shuffle only some elements of a list

Question

I\'m trying to shuffle only elements of a list on 3rd till last position so the 1st two will always stay in place e.g.

list = [\'a?\',\'b\',\'c\',\'d\',\'e\'         


        

Answer 1

To shuffle a slice of the list in place, without copies, we can use a Knuth shuffle:

import random
def shuffle_slice(a, start, stop):
    i = start
    while (i < stop-1):
        idx = random.randrange(i, stop)
        a[i], a[idx] = a[idx], a[i]
        i += 1

It does the same thing as random.shuffle, except on a slice:

>>> a = [0, 1, 2, 3, 4, 5]
>>> shuffle_slice(a, 0, 3)
>>> a
[2, 0, 1, 3, 4, 5]