BTree lengths are too expensive to compute
Objects that use BTrees need to keep track of lengths themselves. This class provides an object for doing this.
As a bonus, the object support application-level conflict resolution.
It is tempting to to assign length objects to __len__ attributes to provide instance-specific __len__ methods. However, this no longer works as expected, because new-style classes cache class-defined slot methods (like __len__) in C type slots. Thus, instance-define slot fillers are ignores.
There are no attributes in this class.
change(delta)
set(v)
There are no known subclasses.