[Python-Dev] Simple generators, round 2

[Samuele Pedroni]

Hi.

> > 2) Do not expose the resume and suspend methods to the
> >    Python user, and recode Generator.py as an extension
> >    module in C. This should prevent abuse of frames.
> 
> I like the frame methods.  However, this may be a good idea since
> Jython may implement things quite differently.

I should repeat this: (if we want to avoid threads for implementing
generators because for them that's really an overkill, especially
if those are used in tight loops): jython codebase have following 
limitations:

- suspensions point should be known at compilation time
 (we produce jvm bytecode, that should be instrumented
  to allow restart at a given point). The only other solution
  is to compile a method with a big switch that have a case
  for every python line, which is quite expensive.
  
- a suspension point can at most do a return, it cannot go up 
  more than a single frame even if it just want to discard them.
  Maybe there is a workaroung to this using exceptions, but they
  are expensive and again an overkill for a tight loop.

=> we can support  something like a supsend keyword. The rest is pain :-( .

regards.