[Python-Dev] New opcode to simplifiy/speedup list comprehensions (original) (raw)

Brett C. bac at OCF.Berkeley.EDU
Sat Mar 6 15:47:53 EST 2004

Raymond Hettinger wrote:

If there are no objections, I would like to add an opcode for calling PyListAppend(). This simplifies the generated code for list comprehensions and reduces the overhead on each pass, improving the timings by about 35% on [i for i in itertools.repeat(None, 500)].

The patch is amazingly brief and clear: www.python.org/sf/910929

Ah, nuts! That was going to be part of my thesis! =) I was going to along the lines of "Type-specific Opcodes for Python Based on Static Type Inferencing of Local Variables". At this rate the the first four words won't be needed. =)

Joking aside, I am +1 since I was planning on adding that myself as long as my thesis pans out and actually is a gain.

Oh, and beware the evil cache monkey and his notorious way of making the eval loop not fit in the CPU cache when a single thing is added to it (or at least I remember a comment along those lines last time people tried fiddling with the eval loop).

-Brett

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