On Mon, Aug 3, 2009 at 2:47 PM, r<rt8...@gmail.com> wrote: > On Aug 3, 4:07 pm, 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 >> >> D[K] = V >> >> will raise an exception unless V == D[K]. In 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]. All 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. Before 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. Otherwise, one will need to look at the UserDict module. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
