<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def remove(self, item):
        'Remove first occurence of item.  Raise ValueError if not found'
        i = self.index(item)
        del self._keys[i]
        del self._items[i]