itertools and amazing speed

[deanhystad]

perm_set is a permutations object, a generator like object that creates results on demand. To see how long this takes you could ask for a list. I doubt you have enough memory.

perm_set = list(itertools.permutations(images,9))

That an itertools.permutations object is a generator is mentioned in the documentation when they say permutations is "roughly equivalent to"

def permutations(iterable, r=None):
    # permutations('ABCD', 2) --> AB AC AD BA BC BD CA CB CD DA DB DC
    # permutations(range(3)) --> 012 021 102 120 201 210
    pool = tuple(iterable)
    n = len(pool)
    r = n if r is None else r
    if r > n:
        return
    indices = list(range(n))
    cycles = list(range(n, n-r, -1))
    yield tuple(pool[i] for i in indices[:r])  # <------ The first tuple.
    while n:
        for i in reversed(range(r)):
            cycles[i] -= 1
            if cycles[i] == 0:
                indices[i:] = indices[i+1:] + indices[i:i+1]
                cycles[i] = n - i
            else:
                j = cycles[i]
                indices[i], indices[-j] = indices[-j], indices[i]
                yield tuple(pool[i] for i in indices[:r])   # <------ More tuples
                break
        else:
            return