I agree it would break in such a situation, but I'm not clear on which direction your bias leads you (specifically, which do we get right -- don't use bound methods, or don't use the __getattr__ magic?).

I could fix this by defining "proxy" functions (and some properties) for the whole file interface, rather than just the methods that potentially trigger rollover.  That would lose a little efficiency, but mostly only in reading (calling e.g., f.read() will always result in two function applications; in the current model, after the first call it runs at "native" speed).  It would also lose forward compatibility if the file protocol changes, although I'm not sure how likely that is.

Would you like me to do that?