> A category in which Hom sets form abelian groups and in which you have
> finite direct sums is an "additive category". An "abelian category"
> is one in which, loosely speaking, you have well-behaved short exact
> sequences: every monomorphism fits into a short exact sequence, and
> every epimorphism fits into a short exact sequence. Wikipedia has a
> reasonable definition, I think.
>
> The category of modules over any ring is abelian (but not just the
> category of free modules, as someone has pointed out in
> category_types.py, unless the ring is a field).
Thanks for the background.
> > Note about the patch: to avoid dependencies on the inheritance order
> > between the bases, wouldn't it be more natural to have the default
> > definition of is_abelian in Category?
>
> That sounds like a good idea.
Will do.
> (Although should the default definition be "NotImplemented" or
> "False"? I'm not sure.)
Do we have a consensus for NotImplemented now?
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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