[Python-Dev] PEP 435 -- Adding an Enum type to the Python standard library

[R. David Murray]

On Fri, 12 Apr 2013 11:02:54 -0400, Barry Warsaw <barry at python.org> wrote:
> On Apr 12, 2013, at 03:31 PM, Dirkjan Ochtman wrote:
> >On Fri, Apr 12, 2013 at 2:55 PM, Eli Bendersky <eliben at gmail.com> wrote:
> >>     >>> Colors.blue >= Colors.green
> >>     Traceback (most recent call last):
> >>     ...
> >>     NotImplementedError
> >
> >I like much of this PEP, but the exception type for this case seems
> >odd to me. Wouldn't a TypeError be more appropriate here?
> >
> >Somewhat like this:
> >
> >>>> 'a' - 'b'
> >Traceback (most recent call last):
> >  File "<stdin>", line 1, in <module>
> >TypeError: unsupported operand type(s) for -: 'str' and 'str'
> 
> Interesting.  I'm having a hard time articulating why, but NotImplementedError
> just feels more right to me in this case.

I think TypeError is more consistent with the rest of Python:

>>> object() < object()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unorderable types: object() < object()

You get that automatically if you return NotImplemented from the
comparison methods.  I don't think you should be explicitly raising
NotImplemented.

--David