Request for comments on a design

TomF tomf.sessile at
Sat Oct 23 20:50:03 CEST 2010

On 2010-10-23 01:50:53 -0700, Peter Otten said:

> TomF wrote:
>> I have a program that manipulates lots of very large indices, which I
>> implement as bit vectors (via the bitarray module).   These are too
>> large to keep all of them in memory so I have to come up with a way to
>> cache and load them from disk as necessary.  I've been reading about
>> weak references and it looks like they may be what I want.
>> My idea is to use a WeakValueDictionary to hold references to these
>> bitarrays, so Python can decide when to garbage collect them.  I then
>> keep a key-value database of them (via bsddb) on disk and load them
>> when necessary.  The basic idea for accessing one of these indexes is:
>> _idx_to_bitvector_dict = weakref.WeakValueDictionary()
> In a well written script that cache will be almost empty. You should compare
> the weakref approach against a least-recently-used caching strategy. In
> newer Pythons you can use collections.OrderedDict to implement an LRU cache
> or use the functools.lru_cache decorator.

I don't know what your first sentence means, but thanks for pointers to 
the LRU stuff.  Maintaining my own LRU cache might be a better way to 
go.  At least I'll have more control.


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