Hi, I have been tracing: vfs.py, pypy_interact.py and sandlib.py. Just to make sure that I got it right. * The object RealFile in vfs.py is first used then we know that here is a RealFile on the real system that is the --tmp=directory, the method is also use on python files I can see from my trace? * The join method in RealDir is the key, because it maps (join) the virtual filename to a real filename og real directory So if I want to expand the vfs.py I need to modify RealDir to allow to return RealFile for files that are new, that is that they are not part of names. On files that do exist and I want to write to then, I do not have a clue. As I can see I get the error even then I open the file using open( "myFile", "w"). And because of that I am not sure about my previous statement " So if I want to expand the vfs.py I need to modify RealDir to allow to return RealFile for files that are new, that is that they are not part of names." Regards, Søren Laursen