Just for fun, let’s see if there is any advantage (apart from generating a smaller code) in using either of the approaches to create an unique list. A list of 741 gene IDs and another one with 1322 (that contained all the 741 IDs from the first) were used. Instead of hard coding the lists in the script, normal I/O was used and the files were read automatically. Using a for loop the scripts were run 10 times and the final time averaged.

Here are the results

Using dictionaries 0.08540
Using sets 0.15890

Almost twice as fast for the dictionaries. Why? One thing, and one thing only: Python version. My system’s box default Python is 2.3.4, which has one of the first implementations of set. I have a “personal” Python version 2.5 so the test was redone with the newer Python

Using dictionaries 0.04520
Using sets 0.03770

Ok. That shows a little bit of advantage for sets what is expected. But it shows us that different versions of Python have a huge difference between them. This is a rather crude and simple test, with a small list of entries, but there is a huge gain from version 2.3 to versio 2.5, either in dicts or sets.

For a more comprehensive test and more functions with a similar objective check this page.