[Python-Dev] About dictionary lookup caching (original) (raw)

Brett Cannon brett at python.org
Tue Dec 19 19:53:35 CET 2006

On 12/19/06, Andrea Griffini <agriff at tin.it> wrote:

I'm experimenting with a patch for dictionary lookup caching, the main idea being avoiding the lookup of a constant (conames) in a dictionary if the dictionary didn't change since last lookup. Currently the cache is held in a structure that is parallel to conames (the LOADGLOBAL opcode uses oparg to access the cache slot) and this is wasteful if there are conames entries that are not used for global lookups. Probably I could act at the code object creation time to sort names so that ones used by LOADGLOBAL are at the beginning of conames but this would require inspecting and hacking the already generated opcode. Another case that would IMO be worth optimizing is the LOADATTR lookup when it's done after a LOADGLOBAL (I suspect that in many cases the element being searched will be a module so caching would be simple to implement; for general objects things are way more complex and I see no simple solution for caching dictionary lookups). My opinion is that it would be by far better to do this ordering of conames at compile time but I've no idea where to look for trying to make such a change. Can someone please point me in the right direction ?

For guidance on how the compiler works, see PEP 339 ( http://www.python.org/dev/peps/pep-0339).

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