How can I make my code be a set?

Question

I have a little code that takes a list of objects, and only outputs the items in the list that are unique.

This is my code

def only_once(a):
    retu         


        

Answer 1

If you need to remove any item that is in the list more than once, not just occurences after the first, you can use:

# without using generators / comprehensions
def only_once(iterable):
    seen = set()
    duplicates = set()
    for item in iterable:
        if item in seen:
            duplicates.add(item)
        seen.add(item)
    result = []
    for item in iterable:
        if item not in duplicates:
            result.append(item)
    return result

For general order-preserving duplicate elimination, see unique_everseen in the itertools recipes:

def unique_everseen(iterable, key=None):
    "List unique elements, preserving order. Remember all elements ever seen."
    # unique_everseen('AAAABBBCCDAABBB') --> A B C D
    # unique_everseen('ABBCcAD', str.lower) --> A B C D
    seen = set()
    seen_add = seen.add
    if key is None:
        for element in ifilterfalse(seen.__contains__, iterable):
            seen_add(element)
            yield element
    else:
        for element in iterable:
            k = key(element)
            if k not in seen:
                seen_add(k)
                yield element