[Python-Dev] [Python-checkins] peps: Pre-alpha draft for PEP 435 (enum). The name is not important at the moment, as

[R. David Murray]

On Sat, 23 Feb 2013 08:27:50 -0800, Eli Bendersky <eliben at gmail.com> wrote:
> On Sat, Feb 23, 2013 at 7:57 AM, R. David Murray <rdmurray at bitdance.com>wrote:
> 
> > On Sun, 24 Feb 2013 01:31:09 +1000, Nick Coghlan <ncoghlan at gmail.com>
> > wrote:
> > > On Sun, Feb 24, 2013 at 1:06 AM, Antoine Pitrou <solipsis at pitrou.net>
> > wrote:
> > > > On Sat, 23 Feb 2013 16:02:31 +0100
> > > > Stefan Krah <stefan at bytereef.org> wrote:
> > > >> eli.bendersky <python-checkins at python.org> wrote:
> > > >> > +Ordered comparisons between enumeration values are *not*
> > supported.  Enums are
> > > >> > +not integers!
> > > >>
> > > >> Hmm. I think this limits interoperation with C libraries and
> > prototyping
> > > >> C code.
> > > >
> > > > Agreed, this is a deal-breaker IMO. I'd actually argue that enums are
> > > > not terribly useful apart from interacting with C constants.
> > >
> > > I've argued in the past that we should have a "Named Value" mechanism
> > > *before* we have a proposal to group named constants in some fashion
> > > (such as sequential enums, or binary flag groups). It never gained
> > > much traction, even though it could be more useful in many cases
> > > (think things like being able to tag a file descriptor with the repr
> > > of the object it belongs to)
> > >
> > > After seeing this checkin, I also suggested to Eli and Barry that any
> > > new PEP on this topic should come with a survey of *existing*
> > > pseudo-enums in the standard library, and an explanation of how the
> > > proposal can be used to make those either easier to debug when they
> > > show up in error messages or otherwise make it easier to detect when
> > > you've made a mistake while working with them.
> >
> > See also http://bugs.python.org/issue16801#msg178542 for another use
> > case for named values.
> >
> > I've seen an awful lot of code that uses global variables or class
> > attributes primarily to get name validation on constant values, and I
> > think all of that code would be a prime candidate for using Named Values.
> > Some of them are also enum-like, but many of them are not.  So I'm with
> > Nick on this one.
> >
> 
> Any suggestions for places in the stdlib where enums could come useful will
> be most welcome

Heh.  I wasn't actually speaking about the stdlib in the second
paragraph :)

But, if we had a Named Value facility I would use it in the email library
for header error sub-codes (something I haven't actually introduced yet).

But, speaking of error codes, it would be really nice if the posix error
numbers had a repr that included the name.

--David