How can I check if there is a duplicate list in a list of lists?

Question

I have a list RESULT that contains lists. I want to add a list to RESULT only if it does not exist.

So

input = [1,2,3]
RESULT = [[5,6], [4,5,8]]

Now, RESULT.append(input) that gives

RESULT = [[5,6], [4,5,8], [1,2,3]]

Now if I try to append [5,6] it shouldn't be added as its already there.

I cannot use a set here so what's the alternative ?

Answer 1

def add(data_, value):
    if value not in data_:
        data_.append(value)

data = [[5, 6], [4, 5, 8]]
print(data)  # [[5, 6], [4, 5, 8]]
add(data, [1, 2, 3])
print(data)  # {(5, 6), (4, 5, 8), (1, 2, 3)}
add(data, [5, 6])
print(data)  # {(5, 6), (4, 5, 8), (1, 2, 3)}