@abstractmethod<EOL><INDENT>def similar_items(self, itemid, N=<NUM_LIT:10>):<DEDENT>
pass<EOL>
Calculates a list of similar items

Parameters
----------
itemid : int
    The row id of the item to retrieve similar items for
N : int, optional
    The number of similar items to return

Returns
-------
list
    List of (itemid, score) tuples