'list' object has no attribute 'union'

It seems like you are trying to use the `union` method on a list object. However, the `union` method is not available for lists in Python. The `union` method is used for set objects instead. If you want to combine two lists and remove duplicates, you can convert them to sets and then convert the result back to a list. Here's an example:

list1 = [1, 2, 3]
list2 = [2, 3, 4]

combined_list = list(set(list1).union(set(list2)))

In this example, `combined_list` will contain `[1, 2, 3, 4]`.