How to find difference table of DES S box in sage math?

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I have tried to find difference table of an Sbox in sage but it supports square Sboxes. Is there a way to find the difference table of an Sboxes like DES. Below is the code and the output when I tried to enter two rows of Sbox.

sage: S = SBox(14,4,13,1,2,15,11,8,3,10,6,12,5,9,0,7,0,15,7,4,14,2,13,1,10,6,12,11,9,5,3,8) sage: S.difference_distribution_table() The out put is

32 x 16 dense matrix over Integer Ring (use the '.str()' method to see the entries)

I donot know what is .str() method. Thanks in advance