Defining a list in Python is easy—just use the bracket syntax to indicate items in a list, like this: list_of_ints = [1, 2, 3] Items in a list do not have to all be the same type; they can be ...

An improvement on this is to keep a second list of unique items already seen, and then check that list to see if the item already exists there. def check_duplicate_improved(items): already_seen = {} ...