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

One solution:

def fixed_shuffle(lst):
    unfrozen_indices, unfrozen_subset = zip(*[(i, e) for i, e in enumerate(lst)
                                            if not e.freeze])
    unfrozen_indices = list(unfrozen_indices)
    random.shuffle(unfrozen_indices)
    for i, e in zip(unfrozen_indices, unfrozen_subset):
        lst[i] = e

NOTE: If lst is a numpy array instead of a regular list, this can be a bit simpler:

def fixed_shuffle_numpy(lst):
    unfrozen_indices = [i for i, e in enumerate(lst) if not e.freeze]
    unfrozen_set = lst[unfrozen_indices]
    random.shuffle(unfrozen_set)
    lst[unfrozen_indices] = unfrozen_set

An example of its usage:

class CAnswer:
    def __init__(self, x, freeze=False):
        self.x = x
        self.freeze = freeze

    def __cmp__(self, other):
        return self.x.__cmp__(other.x)

    def __repr__(self):
        return "" % self.x


lst = [CAnswer(3), CAnswer(2), CAnswer(0, True), CAnswer(1), CAnswer(5),
       CAnswer(9, True), CAnswer(4)]

fixed_shuffle(lst)