Raymond Hettinger added the comment: This is the expected behavior. The assignments are made left-to-right. The first use of L2[1] is updated BEFORE the second use as index.
The assignments are equivalent to: ================================== >>> L1 = [1,3,2,4] >>> L2 = [1,3,2,4] >>> tup = L2[L2[1] - 1], L2[1] >>> tup (2, 3) >>> L2[1] = tup[0] >>> L2[L2[1] - 1] = tup[1] >>> L2 [1, 3, 2, 4] Which is the same as you observed ================================= >>> L1 = [1,3,2,4] >>> L2 = [1,3,2,4] >>> L2[1], L2[L2[1] - 1] = L2[L2[1] - 1], L2[1] >>> L2 [1, 3, 2, 4] The core issue is that L2[1] is being used twice during the series of assignments. First it gets updated with L2[1] = 3. Then L2[1] is used again AFTER it has been updated. ---------- nosy: +rhettinger resolution: -> not a bug stage: -> resolved status: open -> closed _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue30729> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
