Question

I’d like to make one list from two separate lists of unique items.

There are other similar questions but there didn’t seem to be any that concerned doing this problem effectively since the lists are a few million items long.

Totally unrelated: am I the only one who hates how the tags suggestion box covers up the “post your question” button?

Answer 1

Use a set.

>>> first = [1, 2, 3, 4]
>>> second = [3, 2, 5, 6, 7]
>>> third = list(set(first) | set(second))      # '|' is union
>>> third
[1, 2, 3, 4, 5, 6, 7]