[Python-Dev] Optimization of Python ASTs: How should we deal with constant values?

[Jeremy Hylton]

On Wed, May 7, 2008 at 11:43 AM, Thomas Lee <tom at vector-seven.com> wrote:
> Nick Coghlan wrote:
>
> >
> > As Thomas mentions in a later message, making it possible to annotate
> nodes would permit Functions to be annotated as being a generator at the AST
> stage (currently it is left to the bytecode compiler's symtable generation
> pass to make that determination).
> >
> > Although I guess an alternative solution to that would be to have separate
> AST nodes for Functions and Generators as well...
> >
> >
>  I've actually backtracked a little and gone back down the Const path again.
> I know this is the third time I've changed my mind, but it's primarily
> because annotations tend to get a little clunky (or my implementation was,
> at least). Using Const nodes feels a lot more natural inside the optimizer.
> I think it's going to stick, at least in the short term.
>
>  Rather than separate FunctionDef and GeneratorDef nodes, I think a new bool
> attribute (is_generator?) on FunctionDef should do the job nicely. Further,
> I'm thinking we can move the "generator detection code" from the symtable
> into Python/ast.c so the generator/function information is available to the
> optimizer.

Does the optimizer run after the symtable?  I'd expect the symbol
table information to be essential for almost all analysis, so it
should be fine to wait until that pass to mark the generators.

Jeremy

>  This is made a little tricky by the absence of the contextual information
> available that is normally available when flagging generators in the
> symtable. When generating AST nodes for a suite, we know nothing about the
> parent node in which the suite resides. Still, it might be doable. If this
> winds up being ugly, we might need to fall back to the original plan of a
> separate pass over function bodies to detect yield expressions.
>
>  I'll look into all this tomorrow night, along with any other crazy
> suggestions. For now I need to sleep a few hours. :)
>
>  Thanks for the feedback, it's much appreciated.
>
>  Cheers,
>  T
>
>