I think msg213138 has the key: importlib is actually getting frozen in the Python sense of the module's bytecode being included in a C file and then compiled, not just copied into a zip file. When we freeze importlib._bootstrap as _frozen_importlib, importlib is brought along for the ride as well. So when Python code imports it, it's loading from the frozen copy, and __file__ is not defined.

I think I can see how to fix this in cx_Freeze.