New submission from Terry J. Reedy: https://docs.python.org/3/faq/programming.html#why-does-22-10-return-3 "Why does -22 // 10 return -3? It’s primarily driven by the desire that i % j have the same sign as j. If you want that, and also want:
i == (i // j) * j + (i % j) then integer division has to return the floor. C also requires that identity to hold, and then compilers that truncate i // j need to make i % j have the same sign as i. There are few real use cases for i % j when j is negative. When j is positive, there are many, and in virtually all of them it’s more useful for i % j to be >= 0. If the clock says 10 now, what did it say 200 hours ago? -190 % 12 == 2 is useful; -190 % 12 == -10 is a bug waiting to bite." A user noticed that '-190 % 12 == -10' is False, but would be True is '-' were inserted before '12', and posted https://github.com/python/cpython/pull/2768 to correct the presumed typo. It is not a typo, and I will close the issue, but the text as is is confusing. I propose replace "-190 % 12 == -10 is" with "if -190 % 12 were the mathematically equivalent -10, it would be" [a bug waiting to bite]. I don't like the 'bug' part because it would not be a bug, exactly, but it would be bug bait. I am not sure how to improve it though. ---------- assignee: docs@python components: Documentation messages: 299023 nosy: docs@python, terry.reedy priority: normal severity: normal stage: patch review status: open title: Clarify programming faq. type: enhancement versions: Python 3.6, Python 3.7 _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue31021> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
