build_anti_testset() takes along time and at the end it doesnot work

1- reader = Reader(rating_scale=(1, 5)) 2- data = Dataset.load_from_df(ratings[['userId', 'asin', 'rating']], reader) # this is my own dataset 3 - svd = SVD(n_factors= 30 , n_epochs= 20 , lr_all = 0.005 , reg_all = 0.02 ) 4 - real_trainset = data.build_full_trainset() 5 - svd.fit(real_trainset) 6 -real_testset = real_trainset.build_anti_testset() # the code stop here after along time and at the end it returns memory error
7 -predictions = svd.test(real_testset) 8 - top_n = get_top_n(predictions, n=20)

When I run the program it stops at line number 6 because of (build_anti_testset()) and it returns memory error after along time

however when I replace (build_anti_testset()) with (build_testset()) it works and doesnot have any problem

but I need to use (build_anti_testset()) instead of (build_testset()) because I need the predictions to be on the items that the users has not rated yet