In <mailman.4183.1249336823.8015.python-l...@python.org> Chris Rebert <c...@rebertia.com> writes:
>On Mon, Aug 3, 2009 at 2:47 PM, r<rt8...@gmail.com> wrote: >> On Aug 3, 4:07=C2=A0pm, kj <no.em...@please.post> wrote: >>> I use the term "no-clobber dict" to refer to a dictionary D with >>> the especial property that if K is in D, then >>> >>> =C2=A0 D[K] =3D V >>> >>> will raise an exception unless V =3D=3D D[K]. =C2=A0In other words, D[K] >>> can be set if K doesn't exist already among D's keys, or if the >>> assigned value is equal to the current value of D[K]. =C2=A0All other >>> assignments to D[K] trigger an exception. >>> >>> The idea here is to detect inconsistencies in the data. >>> >>> This is a data structure I often need. =C2=A0Before I re-invent the >>> wheel, I thought I'd ask: is it already available? >>> >>> TIA! >>> >>> kynn >> >> Not sure if something like this already exists, but it would be >> trivial to implement by overriding dict.__setitem__() >That is, if you don't care about .update() not preserving the >invariant. The implication here is that .update() does not in turn use .__setitem__(), which I find a bit surprising. kynn -- http://mail.python.org/mailman/listinfo/python-list
