Very nice man
EDIT:I was playing with your code and found out that when the pop up pops ( ) you cant click the slot. To solve this you just need to add 0.01 to its position.
if self.item_under_mouse >=0 and self.drag_item < 0:
txt = self.items[self.item_under_mouse].get_info()
self.informer.show(txt, (x+.01, 0, y+.01), bound = self.bg_size)
elif self.slot_under_mouse >=0:
txt = self.slots[self.slot_under_mouse].get_info()
self.informer.show(txt, (x+.01, 0, y+.01), bound = self.bg_size)
on line 361