On Thu, Aug 27, 2009 at 4:05 PM, Kreso<kkumnotthi...@thatsearchenginesguglsemail.com> wrote: > > I am writing an application that essentially calculates set of numbers, > say N1, N2, ..., where they can be calculated by several different > algorithms. (One should be able to choose the algorithm at run time.) > In each algorithm one starts from a set of functions, say f1, f2, ..., > which are then transformed into some other functions g1(f1, f2, ..), > g2(f1, f2, ...), ... , then maybe transformed once more and result is > obtained by evaluating final functions. > I can naturally think about this as a collection of transformation > blocks, which have functions as input and output, and which can be > put together to get the final results. However, I am not sure > how to program this, especially since one cannot subclass function > type. To be clear let me give simplified example of what is needed: > > f(x) has unknown shape, so one would like to try, say > > f1(x) = ax - b x**2 or f2(x) = a sin(b*x), > > where a and b are variable parameters. > > Then, one would like to create, with known k(x,y), function g(x) > in one of two ways: > > g1(x) = k(x, x)*f(x) or g2(x) = integrate(k(x, y) * f(y), y=0..1), > > and finally evaluate N=g(1) as result. In this simple example > there are 4 different algorithms for f(x) -> g(x) -> N, and one > should be able to simply choose between them, e.g. by calling > N(g1, f2, (a,b)). > > In practice algorithm is not necessary so linear, but is > generally tree-lika: > > (a,b) -> f1(x) --->g1(x)---+ > |--> h(x) --> N > (c,d) ---+--> g2(x)--------+ > | > f2(x) --+ > > > It would be nice to have some class of function-objects, > that f1(x), .., g1(x), ... could be members/instances of so that common > operations on these functions could be possible (checking > that they satisfy some necessary properties, plotting them, ...), > and then second "class" of transformations/methods operating on > these objects. > I seem to be confused by the fact that I would like to somehow treat > algorithms as objects (so that one can experiment with different > algorithm systems) but I don't have clear picture how to do it. > I am just brainstorming for ideas. Any advice is welcome.
It sounds like you're describing the Strategy Pattern (http://en.wikipedia.org/wiki/Strategy_pattern). To have objects callable like functions, just implement the __call__ special method in your class(es): http://docs.python.org/reference/datamodel.html#object.__call__ Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
