[Python-Dev] Switch statement (original) (raw)

Talin talin at acm.org
Sat Jun 24 06:36:47 CEST 2006

Guido van Rossum wrote:

That sounds like a good solution all around. I hope that others can also find themselves in this.

(1) An expression of the form 'static' has the semantics of evaluating the atom at the same time as the nearest surrounding function definition. If there is no surrounding function definition, 'static' is a no-op and the expression is evaluated every time. [Alternative 1: this is an error] [Alternative 2: it is evaluated before the module is entered; this would imply it can not involve any imported names but it can involve builtins] [Alternative 3: precomputed the first time the switch is entered]

I'm thinking that outside of a function, 'static' just means that the expression is evaluated at compile-time, with whatever symbols the compiler has access to (including any previously-defined statics in that module). The result of the expression is then inserted into the module code just like any literal.

So for example:

a = static len( "1234" )

compiles as:

a = 4

...assuming that you can call 'len' at compile time.

The rationale here is that I'm trying to create an analogy between functions and modules, where the 'static' declaration has an analogous relationship to a module as it does to a function. Since a module is 'defined' when its code is compiled, that would be when the evaluation occurs.

I'm tempted to propose a way for the compiler to import static definitions from outside the module ('static import'?) however I recognize that this would greatly increase the fragility of Python, since now you have the possibility that a module could be compiled with a set of numeric constants that are out of date with respect to some other module.

-- Talin

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