Many paths in pythonrun.c contains these lines:
    m = PyImport_AddModule("__main__");
    d = PyModule_GetDict(m);
both return borrowed references, from sys.modules.
in most cases, d is simply passed to PyEval_EvalCode() and not used afterwards, *except* in PyRun_SimpleFileExFlags which calls PyDict_DelItemString(d, "__file__"); this is where the crash occurs.