[Python-Dev] genexps slow? (original) (raw)

Tim Peters tim.one at comcast.net
Mon Apr 5 14:45:51 EDT 2004

[Tim Peters]

There's a twist there: the functions synthesized for generator expressions get to take the quicker-than-general "fastyield" exit path. Hmm! It looks like tests against WHYYIELD before the fastyield label can no longer succeed, but are still there to slow down non-generator cases.

[Michael Hudson]

Hmm. I think I agree with you. I also think the tests against WHYYIELD in the code for ENDFINALLY are unnecessary,

I meant that one too: all tests against WHY_YIELD physically preceding the fast_yield label appear unnecessary now. The only obvious assignment of WHY_YIELD to "why" appears in YIELD_VALUE now, and that jumps immediately to fast_yield, from which there's no going backwards. do_raise() can't return WHY_YIELD either.

as we (syntactically) don't allow yields when there are finally: statements in play.

Even if we did, a yield doesn't collapse any pending block structure.

If I'm wrong about that, then you're wrong too :-) It's all a bit subtle, to be sure.

Na . I'll toss in some asserts and check it in if nothing blows up.

Once again, I wonder if there was someway we could have two evalframes: one with tracing support, one without. Unfortunately, I don't think this can fly (how do you start tracing?). Maybe we could have a '-notrace' command line flag? But I suspect that this is a silly over-complication.

Me too.

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