Harmut, thanks for the status update!

Victor, the problem is that both sys.warnoptions and sys._xoptions get read by Py_Initialize(), so setting them afterwards is essentially pointless - while you do still change the contents of the sys attributes, doing so doesn't have any further effect.

In 3.8, we'll hopefully make an updated version of PEP 432 public, and hence be able to deprecate calling them prior to Py_InitializeCore, and either advise folks to use the the new config structs instead, or else adjust the way that _PySys_BeginInit and _PySys_EndInit work so that the relevant sys module attributes get created in Py_InitializeCore rather than in Py_InitializeMainInterpreter.