Listctrl SetItemData as String

Question

I am not understanding why I can't use a string for SetItemData in a ListCtrl. I use it for a CustomTreeControl and it works fine. I don't get it.

"TypeError: ListCtrl.SetItemData(): argument 2 has unexpected type 'str'"

list_row = self.lc_results.GetItemCount()
self.lc_results.SetItemData(list_row, item.split(':')[1])