On Thu, Aug 14, 2003 at 11:52:55PM -0400, Casey Duncan wrote:
>  > To explain a tiny bit further, I'm using an OOBTree that maps
>  > dictionaries to objects. This is part of the indexing mechanism in
>  > IndexedCatalog, which is a simple indexing and query mechanism for the
>  > ZODB. This allows us to do queries like:
>  > 
>  >     "5 in mydict"
>  
>  I'm not sure how using dictionaries as keys helps here (it just sounds evil to 
>  me ;^), but this is one place where the Python hashing rules for dictionary 

I'm suffering from lack of oxygen (hopefully). The important query here
is, or course:

    "mydict == {foo: bar}"

-- which is handled correctly (AFAICT, and I can't tell much yet because
I still need to test a lot) by simple comparison.

>  keys begin to make lots of sense. In Python you are forbidden from using 
>  simple mutable objects as keys since generating a stable hash for them is not 
>  possible unless you subclass and supply your own hash.
>  
>  BTrees make it much easier to shoot yourself in the foot since keys must only 
>  be comparible, which mutable objects usually are. So the thing to note (no 
>  doubt you have realized this) is that when you use mutable objects as BTree 
>  keys (or set members) you are playing with fire and your are very likely to 
>  get burned.

I'm keeping a close eye on this particular feature to see how well this
hack holds out. It may be that we'll just revert to sequential scans and
go on with life.

>  > I've fixed this to make sure I only store dictionaries as keys. My
>  > wrapper class makes sure that the dicts are never mutated while being
>  > used as being keys, and so far check() has been reassuring.
>  
>  Sounds like mongo pain for a "minor feature".
> 
>  hoping-the-bandages-and-grafts-heal-soonly y'rs,

Well, I didn't mention I had to implement this for lists too! 

(And to think all this because nobody on python-dev lets me work on
fixing LC_NUMERIC. I should get a night job.)

Take care,
--
Christian Reis, Senior Engineer, Async Open Source, Brazil.
http://async.com.br/~kiko/ | [+55 16] 261 2331 | NMFL

_______________________________________________
For more information about ZODB, see the ZODB Wiki:
http://www.zope.org/Wikis/ZODB/

ZODB-Dev mailing list  -  ZODB-Dev@[...].org
http://mail.zope.org/mailman/listinfo/zodb-dev