In the example as written that's not too much of a difference but I find I like the reminder that it's a set which the .difference() call provides, and it allows me to be lazy about converting the second argument to a set first since difference will also accept a list, tuple, generator, Django values_list(), etc.
Comment
I like the solution you ultimately ended up with but tend to write it in this form:
```
new_all_ids = set(all_ids).difference(to_process_ids)
```
In the example as written that's not too much of a difference but I find I like the reminder that it's a set which the .difference() call provides, and it allows me to be lazy about converting the second argument to a set first since difference will also accept a list, tuple, generator, Django values_list(), etc.