Using String Methods In Jump Tables

[Jon Clements]

On 20 Aug, 01:51, Tim Daneliuk <tun... at tundraware.com> wrote:
> On 8/19/2010 7:23 PM, Steven D'Aprano wrote:
>
> > On Thu, 19 Aug 2010 18:27:11 -0500, Tim Daneliuk wrote:
>
> >> Problem:
>
> >>   Given tuples in the form (key, string), use 'key' to determine what
> >>   string method to apply to the string:
>
> >>>> table = {'l': str.lower, 'u': str.upper}
> >>>> table['u']('hello world')
> > 'HELLO WORLD'
>
> Aha!  That's just what I was looking for.
>
>
>
> > [...]
> >> As I said, I know I could do this as a set of cascading ifs or even as
> >> an eval, but I'm loathe to use such approaches. I like jump tables as a
> >> structural construct because they are easy to understand and maintain. I
> >> also realize that what I'm asking may be violating some deeply held
> >> notion of OO purity, but, well, now I'm just curious if there is a way
> >> to do this
>
> > This is Python, not some "pure" OO language. We have functional
> > programming constructs, procedural constructs, and probably other
> > programming models as well. Screw the deeply held notion of OO purity :)
>
> Yeah, I've never been much impressed with the OO purists.  One of
> the best speeches on the subject I ever saw was by David Korn (of
> ksh fame) who did a presentation at USENIX one year called "Objecting
> To Objects".  He documented an attempt to write a compiler using
> purely OO constructs and the many rings of hell that ensued.  
>
>
>
> > But seriously, Python's object model includes bound and unbound methods
> > precisely so you can do this sort of thing, and the above table-based
> > approach is very common and recommended as an alternative to case/switch
> > statements. It's a very common Pythonic idiom, so never fear that people
> > will stone you for using it.
>
> +1
>
>
>
> > The only thing that is a bit unusual is that you call it a jump table. In
> > my experience, "Jump Table" is used for low-level languages where the
> > table values are memory addresses.
>
> Yeah ... those old assembler memories never quite fade do they.
> I dunno what you might call this.  A Function Dispatch Table
> perhaps?
>
> Thanks to both you and Chris for setting me straight :)
>
> --
> ------------------------------------------------------------------------
> Tim Daneliuk
> tun... at tundraware.com

Another more generic option would be to use methodcaller from the
operator module.

Just my 2p,

Jon.