[Python-Dev] Switch statement

Wed Jun 21 19:53:42 CEST 2006

Guido van Rossum wrote:
> But in most cases the 'constant' is actually an expression involving a
> global, often even a global in another module. (E.g. sre_compile.py)
> The compiler will have a hard time proving that this is really a
> constant, so it won't optimize the code.

unless we come up with a way to make it possible to mark an variable as 
a constant.
> The proposed switch semantics (create the table when the containing
> function is defined) get around this by "defining" what it means by
> "constant".

well, given that people find it really confusing that the two X:es in
 def func(value=X):
 print X
are evaluated at different times, I'm not sure it's a good idea to 
introduce more "evaluation scopes".
but sure, I'm sure people doing certification tests would love questions 
like:
 Q: If a program calls the 'func' function below as 'func()'
 and ONE and TWO are both integer objects, what does 'func'
 print ?
 ONE = 1
 TWO = 2
 def func(value=ONE):
 switch value:
 case ONE:
 print value, "is", ONE
 case TWO:
 print value, "is", TWO
 a: "1 is 1"
 b: "2 is 2"
 c: nothing at all
 d: either "1 is 1" or nothing at all
 e: who knows ?
but I cannot say I find it especially Pythonic, really...
</F>