New submission from Terry J. Reedy: Proposal from SO: in the iteration loop for 'myset.difference(iterable)', add equivalent of "if not myset: break'. https://stackoverflow.com/questions/39378043/why-does-pythons-set-difference-method-take-time-with-an-empty-set
In the toy example for testing that this is currently not so, myset starts empty, but it was noted by the OP that a more realistic example would be that myset becomes empty after deletions. Postulated reasons why not to do this (as opposed to why it has not been done yet ;-): 1) averaged over all uses, the time saved not iterating would be less than the time spent testing emptyness. 2) an implicit guarantee to complete the iteration for possible side-effects. One answer notes that myset.difference(anotherset) is special-cased and faster than the equivalent non-set iterable. I searched the tracker for 'empty set difference' and got no hits. If I remember, I will post any disposition of this issue back to SO. ---------- messages: 275707 nosy: rhettinger, terry.reedy priority: normal severity: normal stage: needs patch status: open title: Stop set.difference when set is empty type: performance versions: Python 3.6, Python 3.7 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue28071> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
