[ZODB-Dev] [BTrees] Inconsistent equality checks

[Dieter Maurer]

Tim Peters wrote at 2003-11-6 16:38 -0500:
 > ...
 > > Looking for an alternative, I met the following inconsitency:
 > >
 > > 	a= OOSet((1,2,3))
 > > 	b= OOSet((1,2,3))
 > > 	a.keys() == b.keys()
 > > 	--> 1
 > >
 > > 	a= OOTreeSet((1,2,3))
 > > 	b= OOTreeSet((1,2,3))
 > > 	a.keys() == b.keys()
 > > 	--> 0
 > >
 > > We have the same inconsistency for "OOBucket", "OOBTree" and
 > > "items".
 > 
 > The result type of keys() has to implement IReadSequence, but the
 > IReadSequence interface doesn't define anything about comparability.  What
 > you've determined here is that a Python list (returned by Bucket and Set
 > keys/items/values) implements a different notion of comparison than does a
 > BTreeItems object (returned by BTree and TreeSet keys/items/values).

That's a nice implementation centric explanation of what I found out.

However, from a semantics point of view "OOSet" and "OOTreeSet"
are two implementations of the same abstract data type.
It is therefore surprising that their "keys()" result behave
semantically different with respect to "==".


-- 
Dieter