[Python-Dev] collections module (original) (raw)

Tim Peters tim.one at comcast.net
Tue Jan 13 16:03:29 EST 2004

[Michael Chermside]

... I'm sure this is just pointing out the obvious, but IF the list header were increased, we could add TWO fields... According to Tim, this would still "only" bump list objects up to 24 bytes, but ...

There's something else to note here, in connection with the realloc-avoiding list patch/hack I posted yesterday: for that logic to work, a non-empty list must always contain enough slots for roundupsize(ob->size) elements. So, for example, a list of length 1 must nevertheless contain room for 8 objects, which on a 32-bit machine is 7*4 = 28 bytes in the list guts it doesn't need today (but does need after that patch).

So if people like that patch, it would be more memory-efficient too to drop the roundupsize() business and just expand the list header to remember how many slots have been allocated. Then no overallocation would be needed. Adding 8 bytes in the list header should be a net win over asking for up to 28 unused bytes in the guts (of small lists; it can be larger than that for large lists).

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