[issue22237] sorted() docs should state that the sort is stable
New submission from Wilfred Hughes: According to https://wiki.python.org/moin/HowTo/Sorting/#Sort_Stability_and_Complex_Sorts and Alex Martelli: http://stackoverflow.com/q/1915376/509706, Python's sorted() is stable. It would be great to update the docs for sorted() to state this. ---------- assignee: docs@python components: Documentation messages: 225574 nosy: Wilfred.Hughes, docs@python priority: normal severity: normal status: open title: sorted() docs should state that the sort is stable type: enhancement versions: Python 2.7, Python 3.1, Python 3.2, Python 3.3, Python 3.4, Python 3.5 _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue22237> _______________________________________
Georg Brandl added the comment: I agree: The docs for list.sort() do guarantee the stability, so sorted() should have the same indication. ---------- nosy: +georg.brandl _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue22237> _______________________________________
Changes by Raymond Hettinger <raymond.hettinger@gmail.com>: ---------- assignee: docs@python -> rhettinger nosy: +rhettinger _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue22237> _______________________________________
Martin Panter added the comment: It looks like a fork of that how-to is actually part of the documentation: <https://docs.python.org/release/3.4.0/howto/sorting.html>. Perhaps the two should be linked better. If “sorted” is indeed meant to be stable, that makes the docstring for the “heapsort” function <https://docs.python.org/release/3.4.0/library/heapq.html#basic-examples> invalid. That function is not stable, for example: heapsort((0, 0, False, 0)) -> [0, False, 0, 0]. Also, the how-to implicitly guarantees that only less-than (__lt__) is required for comparison. This is already documented for “list.sort”, but it might be good to add that guarantee to the “sorted” reference. Maybe also clarify if it applies (or not) to other sorting and comparison routines (e.g. heapq, bisect, min, max), though maybe that is straying off scope for this bug. ---------- nosy: +vadmium _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue22237> _______________________________________
Raymond Hettinger added the comment: I'll update the docs for sorted(). ---------- priority: normal -> low versions: -Python 3.1, Python 3.2, Python 3.3 _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue22237> _______________________________________
Stéphane Wirtel added the comment: For this issue, I have read the source code of "sorted" and "list.sort" to be sure they use the same algorithm (not sure). But in the builtin_sorted function, I read PyId_sort, but when I grep the code, I don't find it. Where can I find the reference of this function? Thank you. ---------- nosy: +matrixise _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue22237> _______________________________________
Georg Brandl added the comment: PyId_sort is not a function, it's a somewhat complicated way of getting a Python string "sort" (in this case, for looking up a method using PyObject_GetAttrId). The string object is cached, with is faster than constructing one every time with PyObject_GetAttrString. ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue22237> _______________________________________
Mark Dickinson added the comment:
when I grep the code, I don't find it
The non-greppability is due to preprocessor evil. The culprit is this macro from Include/object.h: #define _Py_IDENTIFIER(varname) _Py_static_string(PyId_##varname, #varname) along with the declaration _Py_IDENTIFIER(sort); earlier in bltinmodule.c. ---------- nosy: +mark.dickinson _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue22237> _______________________________________
Stéphane Wirtel added the comment: Hi Mark, Without your explanation, I was really lost. Thank you. ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue22237> _______________________________________
Stéphane Wirtel added the comment: My patch for the documentation of Python 3.5, just need a small feedback. If you agree with this patch, I will provide the same patch for 2.7 and 3.4 Thank you ---------- keywords: +patch Added file: http://bugs.python.org/file36933/issue22237.patch _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue22237> _______________________________________
Stéphane Wirtel added the comment: ping. ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue22237> _______________________________________
Martin Panter added the comment: The new text seems reasonable to me on its own, however I still think the heapsort() docstring needs updating as well ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue22237> _______________________________________
Roundup Robot added the comment: New changeset d44f7d229e00 by Ezio Melotti in branch '2.7': #22237: document that sorted() is guaranteed to be stable. Initial patch by Martin Panter. https://hg.python.org/cpython/rev/d44f7d229e00 New changeset 5dd4906daa62 by Ezio Melotti in branch '3.4': #22237: document that sorted() is guaranteed to be stable. Initial patch by Martin Panter. https://hg.python.org/cpython/rev/5dd4906daa62 New changeset b01568e2597e by Ezio Melotti in branch 'default': #22237: merge with 3.4. https://hg.python.org/cpython/rev/b01568e2597e ---------- nosy: +python-dev _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue22237> _______________________________________
Ezio Melotti added the comment: Fixed, thanks for the patch! ---------- assignee: rhettinger -> ezio.melotti nosy: +ezio.melotti resolution: -> fixed stage: -> resolved status: open -> closed _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue22237> _______________________________________
Roundup Robot added the comment: New changeset af8f678a4a75 by Ezio Melotti in branch '2.7': #22237: fix patch attribution. https://hg.python.org/cpython/rev/af8f678a4a75 New changeset 2f697bcc8f86 by Ezio Melotti in branch '3.4': #22237: fix patch attribution. https://hg.python.org/cpython/rev/2f697bcc8f86 New changeset 7e870ddd1989 by Ezio Melotti in branch 'default': #22237: merge patch attribution fix. https://hg.python.org/cpython/rev/7e870ddd1989 ---------- _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue22237> _______________________________________
participants (8)
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Ezio Melotti -
Georg Brandl
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Mark Dickinson
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Martin Panter
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Raymond Hettinger
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Roundup Robot
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Stéphane Wirtel
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Wilfred Hughes