On 15.02.2014 07:03, Stephen J. Turnbull wrote: > M.-A. Lemburg writes: > > > IMO, it was a mistake to have None return a TypeError in > > comparisons, since it makes many typical data operations > > fail, e.g. > > I don't understand this statement. The theory is that they *should* > fail. > > The example of sort is a good one. Sometimes you want missing values > to be collected at the beginning of a list, sometimes at the end. > Sometimes you want them treated as top elements, sometimes as bottom. > And sometimes it is a real error for missing values to be present. > Not to mention that sometimes the programmer simply hasn't thought > about the appropriate policy. I don't think Python should silently > impose a policy in that case, especially given that the programmer may > have experience with any of the above treatments in other contexts.
None is special in Python and has always (and intentionally) sorted before any other object. In data processing and elsewhere in Python programming, it's used to signal: no value available. Python 3 breaks this notion by always raising an exception when using None in an ordered comparison, making it pretty much useless for the above purpose. Yes, there are ways around this, but none of them are intuitive. Here's a particularly nasty case: >>> l = [(1, None), (2, None)] >>> l.sort() >>> l [(1, None), (2, None)] >>> l = [(1, None), (2, None), (3, 4)] >>> l.sort() >>> l [(1, None), (2, None), (3, 4)] >>> l = [(1, None), (2, None), (3, 4), (2, 3)] >>> l.sort() Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unorderable types: int() < NoneType() -- Marc-Andre Lemburg eGenix.com Professional Python Services directly from the Source (#1, Feb 17 2014) >>> Python Projects, Consulting and Support ... http://www.egenix.com/ >>> mxODBC.Zope/Plone.Database.Adapter ... http://zope.egenix.com/ >>> mxODBC, mxDateTime, mxTextTools ... http://python.egenix.com/ ________________________________________________________________________ 2014-02-12: Released mxODBC.Connect 2.0.4 ... http://egenix.com/go53 ::::: Try our mxODBC.Connect Python Database Interface for free ! :::::: eGenix.com Software, Skills and Services GmbH Pastor-Loeh-Str.48 D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg Registered at Amtsgericht Duesseldorf: HRB 46611 http://www.egenix.com/company/contact/ _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
