[Python-Dev] PEP 372 -- Adding an ordered directory to collections ready for pronouncement

[Scott David Daniels]

Forest wrote:
> On Tue, March 3, 2009 11:20 am, Forest wrote:
>> Okay, but I'd also like a convenient and fast way to find the oldest entry
>> in an OrderedDict, which I think I'd need for an LRU cache.  Skimming the
>> current patch (od7.diff), I didn't notice one.  Perhaps I simply missed
>> something.  Shouldn't popitem() allow the caller to choose which end from
>> which to pop?
> 
> Thinking it through a bit more, and LRU cache would actually need to
> access the oldest item before knowing whether to remove it.  Besides,
> popitem() should probably retain the signature of dict.popitem().  I
> therefore retract my suggestion about popitem().
> 
> Still, I think an LRU cache would be a very common use case for an ordered
> dict.  The current implementation already uses a list to keep track of
> order, which makes accessing the oldest key a simple matter of exposing
> it.  Perhaps a new method like getfirst() would be worth while here?

But you must decide if what you want really does LRU -- does accessing
the oldest entry make it the most recent entry?

--Scott David Daniels
Scott.Daniels at Acm.Org