'Return a list of recommended items, ordered from most strongly
recommend to least.
Parameters
user_id: int or string
User for which recommendations are to be computed.
how_many: int
Desired number of recommendations (default=None ALL)'

def recommend(self, user_id, how_many=None, **params):

    self._set_params(**params)
    candidate_items = self.all_other_items(user_id)
    recommendable_items = self._top_matches(user_id, candidate_items, how_many)
    return recommendable_items
