Python 3.0, rich comparisons and sorting order

[Tim Peters]

[Steven Bethard]
>> Is there a good use case for binary trees with incompatible types
at the nodes?

[Jeremy Bowers]
> See the ZODB's BTree-based storage.

If you really look at them, you'll eventually read the "Total Ordering
and Persistence" section of the BTree docs:

<http://zope.org/Wikis/ZODB/FrontPage/guide/node6.html#SECTION000631000000000000000>

It's strongly recommended there that people use a single key type per
BTree instance.  Most of that part of the docs is explaining how many
nasty ways there are to get into bad trouble by being cleverer than
that.