[Python-Dev] switch-based programming in Python

[M.-A. Lemburg]

"Martin v. Loewis" wrote:
> 
> > I don't think you need anything extra if the RHS of the == is a hashable
> > literal of some sort and the LHS is always the same simple variable or
> > subscript expression.  If the compiler can recognize the structure (that may
> > be a big "if"), all you need is a dictionary of offsets stored in the
> > function's constants.  You just execute the equivalent of
> >
> >     offset = jumptable.get(x, E)
> 
> That won't work: It maybe that x is not hashable, even though it
> compares equal with the RHS values.
> 
> Even if it was hashable, you'd change the language semantics: In the
> original code, you call __cmp__, say, 20 times; in the modified code,
> you call __hash__ once and __cmp__ perhaps also once. If __cmp__ has
> side effects, you get a language change.

Good point. 

Now would such a change be acceptable if the optimization would
only be triggered for builtin immuatble types on both sides of
the "==" ?

-- 
Marc-Andre Lemburg
CEO eGenix.com Software GmbH
______________________________________________________________________
Consulting & Company:                           http://www.egenix.com/
Python Software:                        http://www.lemburg.com/python/