dis module https://docs.python.org/2/library/dis.html Documentation does not include BUILD_SET bytecode instruction, although it seems it is present in all Python 2 versions I experimented with. Maybe my reasoning is wrong (maybe BUILD_SET is not considered bytecode inst.), but also maybe there are some other instructions missing. It is present in Python 3 docs. minimal case: import dis def fun(): return {1,2,3,4,5} print dis.dis(fun) output: 49 0 LOAD_CONST 1 (1) 3 LOAD_CONST 2 (2) 6 LOAD_CONST 3 (3) 9 LOAD_CONST 4 (4) 12 LOAD_CONST 5 (5) 15 BUILD_SET 5 18 RETURN_VALUE None Best regards Hrvoje Abraham HRVOJE ABRAHAM Software Development Engineer Advanced Simulation Technologies / CDU hrvoje.abraham@avl.com<mailto:hrvoje.abraham@avl.com> T: +385 1 7775 000, F: +385 1 7775 123 M: +385 99 2380 737, Office: +385 1 7775 068 AVL-AST D.O.O. HR-10020 Zagreb, Strojarska 22 www .avl .com [cid:image001.png@01CF48D8.17AEEF30]<https://www.facebook.com/AVL.List> [cid:image002.png@01CF48D8.17AEEF30] <https://twitter.com/AVL_List> [cid:image003.png@01CF48D8.17AEEF30] <http://www.linkedin.com/company/avl> [cid:image004.png@01CF48D8.17AEEF30] <https://www.xing.com/companies/avllistgmbh> [cid:image005.png@01CF48D8.17AEEF30] <http://www.youtube.com/user/AVLList>