> Surely, if these objects define non-trivial 'close' members, they must 
> not be called during garbage collection.

Define "non-trivial". There are various tests for it in test_io.

Not ending up in gc.garbage is *by design*. Making file objects uncollectable as soon as they appear in a reference cycle would be a serious regression. That's why the cleanup is done in tp_dealloc instead of having a __del__.