Test to check if a list is present inside a python list of lists

Question

Basically, I need to get few permutations of a list. So, the method that I have used is to shuffle the list string randomly to get the permutation and add it to a list, while adding I check if there exists the same permutation in the list. I am not able to implement the check. Here is the code that I have written.

list = [x for x in range(0,max)]
totalperm = 10
perms = []
while(len(perms) <> totalperm):
    random.shuffle(list)        
    if list not in perms:
        perms.append(list)            

Please let me know what am I missing here.

Answer 1

Use python's builtin set to prevent duplicates:

perms = set()
while len(perms) != totalperm:
    random.shuffle(lst)        
    perms.add(tuple(lst))

Answer 2

When you're shuffling the list, you're modifying it in place. Later, you add a reference to it to your list of perms. Next time through your loop, you shuffle the list in place again. If you look at perms, it will contain n references to your original list.

You probably want to do something like this instead:

shuffled = list[:]
random.shuffle(shuffled)
if shuffled not in perms:
    perms.append(shuffled)