[Python-Dev] speeding up list append calls (original) (raw)

Neal Norwitz nnorwitz at gmail.com
Wed Sep 14 07:50:17 CEST 2005

Tim made me do it!

http://groups.google.com/group/comp.lang.python/msg/9075a3bc59c334c9

For whatever reason, I was just curious how his code could be sped up. I kept seeing this append method being called and I thought, "there's an opcode for that." What happens if you replace var.append() with the LIST_APPEND opcode.

standard opcodes

$ ./python ./Lib/timeit.py -n 1000 -s 'import foo' 'foo.foo1(10000)' 1000 loops, best of 3: 3.66 msec per loop

hacked version

$ ./python ./Lib/timeit.py -n 1000 -s 'import foo' 'foo.foo2(10000)' 1000 loops, best of 3: 1.74 msec per loop

The patch and foo.py are attached.

This code doesn't really work in general. It assumes that any append function call is a list method, which is obviously invalid. But if a variable is known to be a list (ie, local and assigned as list (BUILD_LIST) or a list comprehension), could we do something like this as a peephole optimization? I'm not familiar enough with some dynamic tricks to know if it there are conditions that could break this.

Probably useless, but it was interesting to me at the time.

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