<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def similar_items(self, itemid, N=10):
 """ Returns a list of the most similar other items """

        if itemid >= self.similarity.shape[0]:
            return []

        return sorted(list(nonzeros(self.similarity, itemid)), key=lambda x: -x[1])[:N]