The file importlib.h is used when building the Python interpreter but it is *not* available in a standard (non-source) distribution of Python. I have copied the file from a source distribution of Python and that does in fact work, but I don`t want to make use of what is intended to be a private implementation detail. I am the author of cx_Freeze and trying to make it work correctly with Python 3.3. What I am looking for here is what I should be doing instead or asking for API that I can use. I hope that explains things better.