The changes from python/cpython@f2244ea as part of https://bugs.python.org/issue20172 changed the DWORD return value from the GetExitCodeProcess() Win32 API to be correctly interpreted as an unsigned long. That is to say, the code in Python 2.7 previously did

PyInt_FromLong(exit_code)

and was replaced with

return_value = Py_BuildValue("k", _return_value)

(where "k" means unsigned long).