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

def set_item(self,item):
        "For inference, will briefly replace the dataset with one that only contains `item`."
        self.item = self.x.process_one(item)
        yield None
        self.item = None