// @pyswig int|PumpWaitingMessages|Pumps all waiting messages for the current thread.
// @rdesc Returns non-zero (exit code from PostQuitMessage) if a WM_QUIT message was received, else 0
static PyObject *PyPumpWaitingMessages(PyObject *self, PyObject *args)
{
	UINT firstMsg = 0, lastMsg = 0;
	if (!PyArg_ParseTuple (args, "|ii:PumpWaitingMessages", &firstMsg, &lastMsg))
		return NULL;
	// @pyseeapi PeekMessage and DispatchMessage

    MSG msg;
	WPARAM result = 0;
	// Read all of the messages in this next loop, 
	// removing each message as we read it.
	Py_BEGIN_ALLOW_THREADS
	while (PeekMessage(&msg, NULL, firstMsg, lastMsg, PM_REMOVE)) {
		// If it's a quit message, we're out of here.
		if (msg.message == WM_QUIT) {
			if(0 != msg.wParam)
				result = msg.wParam;
			else
				result = 1;
			break;
		}
		// Otherwise, dispatch the message.
		if(NULL == hDialogCurrent || !IsDialogMessage(hDialogCurrent,&msg)) {
			TranslateMessage(&msg);
			DispatchMessage(&msg);
		}
	} // End of PeekMessage while loop
	// @xref <om win32gui.PumpMessages>
	Py_END_ALLOW_THREADS
	return PyWinLong_FromVoidPtr((void *)result);
}

http://blogs.msdn.com/oldnewthing/archive/2005/02/17/375307.aspx