That's a good point.  I don't think there's a way to ensure it is on the same filesystem, other than to create it in the same directory as the real file.  (Not every filesystem is even going to have a `/tmp` area.)  We do run the risk of leaving temporary files in the user's work area that way, but I think the performance benefits are worth that.  And proper use of `try/except/else/finally` here would ameliorate some of that (short of the process being forcibly killed).