ANNOUNCE: PySymbolic - Doing Symbolics in Python

Alex Martelli aleaxit at yahoo.com
Fri Oct 13 09:00:25 CEST 2000


"Tim Peters" <tim_one at email.msn.com> wrote in message
news:mailman.971399443.5181.python-list at python.org...
    [snip]
> >         Diff(x*x,x)
    [snip]
> [Alex Martelli]
> > Python evaluates the arguments before passing them to any
> > callable-object.  So, for example, if you write
> >     Diff(x*x, x)
> > the x*x multiplication will take place before Diff ever sees
    [snip]
> >     Diff('x*x', 'x')
>
> I believe Pearu has already discovered "the right way" to get the effect
> he's after in Python:  define a class for symbolic variables, and precede
> his examples by, e.g.,
>
>     x = Symbolic('x')
>     a = Symbolic('a')
>
> and so on.  Then define Symbolic.__add__ etc to build up an expression
tree.

Aha, I see -- thanks for pointing it out, I had a blind spot there.  Funny
how one gets these blind-spots at times!


> That slick trick has been rediscovered several times in Python, and I've
> found it quite satsifying in practice the few times I've used it.
>
> beats-incessant-quoting-anyway-ly y'rs  - tim

Definitely.  Once again, Python's simplicity, dynamicity, regularity,
combine to make the seemingly-impossible into the actually-pretty-easy.
What a language...!


Alex






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