[issue20630] Add sorting helpers for collections containing None values
Raymond Hettinger added the comment: Currently, it's a bit annoying to sort collections containing None values in Python 3 I think we should seriously consider whether to restore None's ability to compare with other entries. Removing this capability has been a major PITA and is an obstacle for people converting code to Python 3. The need to create helper function work-arounds is a symptom, not a cure. -- nosy: +rhettinger ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue20630 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue20630] Add sorting helpers for collections containing None values
Tim Peters added the comment: I've haven't yet seen anyone complain about the inability to compare None except in the specific context of sorting. If it is in fact specific to sorting, then this specific symptom and the problem are in fact the same thing ;-) -- nosy: +tim.peters ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue20630 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue20630] Add sorting helpers for collections containing None values
Antoine Pitrou added the comment: Both Nick's proposals look ok to me. -- nosy: +pitrou ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue20630 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue20630] Add sorting helpers for collections containing None values
Nick Coghlan added the comment: It occurred to me the current names are a bit misleading when using reverse=True, so low/high is likely a better naming scheme than first/last. I think I'll propose a patch for six before doing anything to the standard library - this is already an issue for some forward ports, so at least adding a none_low sort key that is a no-op on Py2 makes sense. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue20630 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue20630] Add sorting helpers for collections containing None values
Nick Coghlan added the comment: And in case that last comment worried anyone - I won't commit *anything* related to this to the standard library until after creating a PyPI sortlib module that includes both this and an order_by_key class decorator, and we have consensus that the proposed changes are reasonable. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue20630 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue20630] Add sorting helpers for collections containing None values
Raymond Hettinger added the comment:
If it is in fact specific to sorting, then this specific symptom
and the problem are in fact the same thing ;-)
The first rule of tautology club is the first rule of tautology club ;-)
FWIW, we had to add a work-around for this in pprint._safe_key class. Without
that work-around, it was difficult to work with JSON-style data hierarchies:
# wouldn't pprint() without the _safe_key() work-around:
temperatures = {'Jan': 25.2, 'Feb': 22.3, 'Mar': None, 'Apr': 19.1,
'May': 22.2, 'Jun': None, 'July': 22.3}
I think this will be typical for the kind of issue people will encounter when
using None as a placeholder for missing data.
FWIW, if None stays non-comparable, Nick's additions look fine to me. I just
think it easier for everyone to restore None's universal comparability rather
than adding work-arounds for the problems caused by removing that capability.
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[issue20630] Add sorting helpers for collections containing None values
Nick Coghlan added the comment: I suspect if we'd thought of it back in the 3.0 or 3.1 time frame then giving the Py3 None a consistent sorts low behaviour would have been more likely. At this stage of the Py3 life cycle, though, it seems simpler overall to remain consistent with earlier Py3 releases. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue20630 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue20630] Add sorting helpers for collections containing None values
Changes by Arfrever Frehtes Taifersar Arahesis arfrever@gmail.com: -- nosy: +Arfrever ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue20630 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue20630] Add sorting helpers for collections containing None values
Raymond Hettinger added the comment: At this stage of the Py3 life cycle, though, it seems simpler overall to remain consistent with earlier Py3 releases. Given that so few users have converted, it is simpler to become consistent with Py2.7 and to not introduce compensating features. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue20630 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue20630] Add sorting helpers for collections containing None values
Changes by Chris Rebert pyb...@rebertia.com: -- nosy: +cvrebert ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue20630 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue20630] Add sorting helpers for collections containing None values
New submission from Nick Coghlan: Currently, it's a bit annoying to sort collections containing None values in Python 3. While the default behaviour isn't going to change, it would be good to offer standard none_first and none_last helps (inspired by the SQL NULL FIRST and NULL LAST ordering control). Suggested home: functools (since that is where the total_ordering class decorator already lives), but collections would also be a reasonable choice (as this feature mostly relates to sorting containers) The minimal option (suggested by Peter Otten): def none_first(v): return v is not None, v def none_last(v): return v is None, v A more complex alternative would be to provide general purpose SortsFirst and SortsLast singletons: @functools.total_ordering class _AlwaysLesser: def __eq__(self, other): return isinstance(other, _AlwaysLesser): def __lt__(self, other): return not isinstance(other, _AlwaysLesser): @functools.total_ordering class _AlwaysGreater: def __eq__(self, other): return isinstance(other, _AlwaysGreater): def __gt__(self, other): return not isinstance(other, _AlwaysGreater): SortsFirst = _AlwaysLesser() SortsLast = _AlwaysGreater() def none_first(v): return SortsFirst if v is None else v def none_last(v): return SortsLast if v is None else v The advantage of the latter more complex approach is that you can embed the SortsFirst and SortsLast values inside a tuple as part of a more complex key, whereas the simple solution only handles the case where the entire value is None. (Inspired by Chris Withers's python-dev thread: https://mail.python.org/pipermail/python-dev/2014-February/132332.html) -- messages: 211251 nosy: ncoghlan priority: normal severity: normal status: open title: Add sorting helpers for collections containing None values type: enhancement versions: Python 3.5 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue20630 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
