My point is that in five years' time some existing well-tested sysadmin-like program will be run with Python 3.4 for the first time, and suddenly whole systems will break.  I don't want to sound negative but this is the worst behavior ever (with the possible exception of programs that do bad things beyond your own system, like viruses).  Please at least crash with an exception instead: add one easy check to py_compile.compile() and complain if cfile points to an existing non-regular file.