And if you want all of the specified slot options, how about a slotoptionsfull:

Code
machine_type.set("slotoptions", sol::property([this](running_machine &r) {
			std::string result;
			for (device_slot_interface &slot : slot_interface_iterator(r.root_device()))
			{
				if (slot.has_selectable_options())
				{
					std::string specified_value = machine().options().slot_option(slot.slot_name()).specified_value();
					if (specified_value.compare(std::string("")) != 0)
					{
						result += (std::string("-")+std::string(slot.slot_name())+" "+
									specified_value.c_str()+
									std::string("\n"));
					}
				}
			}
			return result;
		}));


	machine_type.set("slotoptionsfull", sol::property([this](running_machine &r) {
			std::string result;
			for (device_slot_interface &slot : slot_interface_iterator(r.root_device()))
			{
//				if (slot.has_selectable_options())
				{
					{
						result += (std::string("-")+std::string(slot.slot_name())+" "+
									machine().options().slot_option(slot.slot_name()).value().c_str()+
									std::string("\n"));									
					}
				}
			}
			return result;
		}));


and trying it out:

Code
[MAME]> print(manager:machine().slotoptions)
-board3:ide:ide:1 hdd
-board4:lpt:lpt:centronics ap2000

[MAME]> print(manager:machine().slotoptionsfull)
-kbd ms_naturl
-board1 fdcsmc
-board1:fdcsmc:fdc:0 35hd
-board1:fdcsmc:fdc:1 35hd
-board2 comat
-board2:comat:serport0 logitech_mouse
-board2:comat:serport1 
-board3 ide
-board3:ide:ide:0 hdd
-board3:ide:ide:1 hdd
-board4 lpt
-board4:lpt:lpt:centronics ap2000
-isa1 svga_et4k
-isa2 
-isa3 
-isa4 
-isa5 

[MAME]>