On 24 Jan 2014 15:57, "Chris Barker - NOAA Federal" <chris.bar...@noaa.gov> wrote: > > >> c = a + b: 3N >> c = a + 2*b: 4N > > Does python garbage collect mid-expression? I.e. : > > C = (a + 2*b) + b > > 4 or 5 N?
It should be collected as soon as the reference gets dropped, so 4N. (This is the advantage of a greedy refcounting collector.) > Also note that when memory gets tight, fragmentation can be a problem. I.e. if two size-n arrays where just freed, you still may not be able to allocate a size-2n array. This seems to be worse on windows, not sure why. If your arrays are big enough that you're worried that making a stray copy will ENOMEM, then you *shouldn't* have to worry about fragmentation - malloc will give each array its own virtual mapping, which can be backed by discontinuous physical memory. (I guess it's possible windows has a somehow shoddy VM system and this isn't true, but that seems unlikely these days?) Memory fragmentation is more a problem if you're allocating lots of small objects of varying sizes. On 32 bit, virtual address fragmentation could also be a problem, but if you're working with giant data sets then you need 64 bits anyway :-). -n
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