The example shown on the Refurb GitHub page is a little unfortunate. As you say, there is also a potential scalability problem with the original design if the i

The example shown on the Refurb GitHub page is a little unfortunate. As you say, there is also a potential scalability problem with the original design if the input file is too large to hold in memory in its entirety. In the example, that issue could be avoided with minimal cost by reading the file lazily: with open(filename) as f: for line in f: do_same_things_with(line) The specific change Refurb suggests instead doesn’t have this benefit. However, in general switching to a lazy design won’t always be as safe and easy as it is here, so I’m not sure what I’d ideally want a tool to say in this situation. You’d need much more sophisticated analysis of the original code’s design if you wanted to do something like warning about unnecessarily reading an entire file and suggesting the lazy alternative. It doesn’t seem like a good idea to warn about all uses of the functions that will read the whole file at once, because often with Python scripts that’s a simple and effective way get the required job done and the added complexity from a more scalable design isn’t needed or justified. Writing good style checkers is hard. :-)