Unable to convert list into set, raises “unhashable type: 'list' ” error

Question

So I\'m trying to find all sub-lists of a list and here is what I have now. I\'m new to Python and I don\'t understand why \" Q3_ans=set(ans)\" raises an error. I\'ve tried

Answer 1

As you can figure out why, mutable types like lists can't be hashable, so can't be converted to a set. You can try returning tuple instead; an immutable counterpart for list:

def f2(seq):
    assert len(seq)==2
    assert isinstance(x, tuple) # what's `x` actually?
    a, b = seq
    return ((a), (b), (a,b))

def all_sublists(x):
    assert isinstance(x, list)
    ans = []
    for i in range(0, len(x) - 1):
        for j in range(1, len(x)):
            temp = (x[i], x[j])
            temp = [f2(temp)]
            ans.extend(temp)
    Q3_ans = set(tuple(ans))
    return Q3_ans

then

all_sublists([1, 2, 3])

You can read more about tuple type in the documentation.