I have a list containing multiple lists as its elements
TypeError: unhashable type: 'list'
TopP = sorted(set(TopP),reverse=True)
Sets require their items to be hashable. Out of types predefined by Python only the immutable ones, such as strings, numbers, and tuples, are hashable. Mutable types, such as lists and dicts, are not hashable because a change of their contents would change the hash and break the lookup code.
Since you're sorting the list anyway, just place the duplicate removal after the list is already sorted. This is easy to implement, doesn't increase algorithmic complexity of the operation, and doesn't require changing sublists to tuples:
def uniq(lst): last = object() for item in lst: if item == last: continue yield item last = item def sort_and_deduplicate(l): return list(uniq(sorted(l, reverse=True)))