Questions about remembering and caching function arguments

[thebjorn]

On Nov 12, 1:05 am, "Anand Patil" <anand.prabhakar.pa... at gmail.com>
wrote:
> Hi all,
>
> I have two questions about a class, which we'll call MyWrapperClass,
> in a package to which I'm contributing.
>
> 1) MyWrapperClass wraps functions. Each instance has an attribute
> called 'value' and a method called 'eval', which calls the wrapped
> function. An instance D that depends on instances A, B and C can be
> created as follows:
>
> @mywrapperclass
> def D(A, B, C):
>     return foo(A.value, B.value, C.value)
>
> Now that D exists, the call D.eval() will work without any arguments
> (D remembers that the arguments are A, B and C and passes their values
> to foo). What is the standard terminology for such classes, and does
> anyone know of a package that implements them in a nice way? (It's
> easy enough to roll our own, but reading about other implementations
> might give us good ideas).
>
> 2) D.eval() will frequently be called multiple times in succession
> before A.value, B.value or C.value has had the chance to change. It
> would be _extremely_ helpful to have D detect this situation and skip
> recomputation. I'm looking for the fastest safe way to do this.
> There's no restriction on what kind of object A.value, etc. are, so
> unfortunately they might be mutable.
>
> Our current solution is to have D compare A.value, B.value and C.value
> to an internal cache using the 'is' operator (and put a big warning in
> the docs about not changing 'value' attributes in-place). Not exactly
> safe, but the speed savings over comparison with '==' will be
> significant. Is this OK, bad or an abomination?
>
> Again it would be helpful to know the terminology associated with the
> behavior I'm looking for and any packages that implement it nicely.
>
> Many thanks in advance and apologies for the long post,
> Anand

Cells (A dataflow extension to CLOS) seems like what you want:

  http://common-lisp.net/project/cells/

I think there was talk of a Python version a while back...

-- bjorn