<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def add(self, item, position=5):
 """Add an item to the list unless it is already present. If the item is an expression, then a semicolon will be appended to it in the final compiled code. """

        if item in self.items:
            return
        self.items[item] = position
        self._add_dep(item)
        self.order = None
        self.changed(code_changed=True)