On 17.02.2014 13:12, Nick Coghlan wrote: > On 17 Feb 2014 21:15, "M.-A. Lemburg" <[email protected]> wrote: >> >> 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. > > This is the first I've ever heard of that sorting behaviour being an > intentional feature, rather than just an artefact of Python 2 allowing > arbitrarily ordered comparisons between different types. Can you point me > to the relevant entry in the Python 2 language reference?
This is not documented anywhere in the language spec, AFAIK. It is documented in the code (Python 2.7; Object/object.c): default_3way_compare(PyObject *v, PyObject *w) ... /* None is smaller than anything */ if (v == Py_None) return -1; if (w == Py_None) return 1; Note that it's not important whether None is smaller or greater than any other object. The important aspect is that it's sorting order is consistent and doesn't raise a TypeError when doing an ordered comparison with other objects. -- 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年02月12日: 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 [email protected] https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com