Check for duplicates in list Checks if there are duplicate values in a flat list. Use set() on the given list to remove duplicates, compare its length with the length of the list. def has_duplicates(lst): return len(lst) != len(set(lst)) x = [1, 2, 3, 4, 5, 5] y = [1, 2, 3, 4, 5] has_duplicates(x) # True has_duplicates(y) # False