<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def move(self, item, new_index):
 """Move an item to the given position. Unique(['eggs', 'spam']) Traceback (most recent call last):
 ValueError: 'ham' is not in list """

        idx = self._items.index(item)
        if idx != new_index:
            item = self._items.pop(idx)
            self._items.insert(new_index, item)