python ‘in’ set vs list

Came across a comment on this Stackoverflow question which concerned converting a list to a set before looking for items in that set.

The point of set is to convert in from an O(n) operator to an O(1) operator. In this case it doesn’t really matter, but for larger data sets it would be inefficient to have multiple linear scans over a list.

Which led me to look a bit more at time complexity in python functions in general.

In the past I would only convert a list to a set if I wanted to remove duplicates. But evidently it’s a good habit to get into if speed of looking in that set is important. Though, obviously, converting list to set is O(n) in the first place.