So that all happens because importlib does an atomic write of the file which uses os.replace(): http://hg.python.org/cpython/file/83d70dd58fef/Lib/importlib/_bootstrap.py#l121 .

Unless there is some way that I can't think of to have the atomic write still exist but not change the type of file it replaces I am still not willing to revert my change just for this use case. There should be a single implementation of bytecode file generation and py_compile (along with compileall) should be nothing more than convenience modules for forcing the generation of those files under the same semantics as if they were done as a side-effect of importing some source code.