Python: shuffling list, but keeping some elements frozen

Question

I\'ve such a problem:

There is a list of elements of class CAnswer (no need to describe the class), and I need to shuffle it, but with one constraint -

Answer 1

In linear time, constant space using random.shuffle() source:

from random import random

def shuffle_with_freeze(x):
    for i in reversed(xrange(1, len(x))):
        if x[i].freeze: continue # fixed
        # pick an element in x[:i+1] with which to exchange x[i]
        j = int(random() * (i+1))
        if x[j].freeze: continue #NOTE: it might make it less random
        x[i], x[j] = x[j], x[i] # swap