CvPopupInfo *pInfo;
pInfo = new CvPopupInfo((BUTTONPOPUP_PYTHON_SCREEN));
pInfo->setText(L"nameOfYourPythonPopup");
// you can give some aditional information to pInfo here and read them in your python screen. Take a look at CvPopupInfo
gDLL->getInterfaceIFace()->addPopup(pInfo, GET_PLAYER(getActivePlayer()).getID(), true, true);