[ZODB-Dev] More ExtensionClass coercion

[Christian Reis]

Jeremy, I see an XXX in the ExtensionClass ChangeLog:

    2003-05-09 16:59  jeremy

    * ExtensionClass/src/Missing.c: Don't coerce Missing.Value to a
      non-numeric type.

    Fixes crash reported by Tres Seaver.  Missing.Value offered to
    coerce itself to unicode.  unicode_compare() blew up because it
    expected that the other argument had been converted to unicode.

    XXX But why does this implement coercion at all?

I've noticed an odd, related, `feature' in Persistent. The following
testcase is what I dug up to demonstrate. It only seems to happen with
*subclasses* of Persistent; Persistent itself works correctly, as do
classes derived from ExtensionClass.Base. Here:

    from ZODB import Persistent
    p = Persistent()
    print 0 == p, p == 0, 0 < p, p > 0, 0 > p, p < 0

Prints out (correctly, afaict):

    0 0 1 1 0 0

Now, see how this changes:

    class Foo(klass): pass
    p = Foo()
    print 0 == p, p == 0, 0 < p, p > 0, 0 > p, p < 0 

Results in:

    1 0 0 1 0 0

This is also a coercion problem, AFAICT. It seems that subclasses of
Persistent have ob_type->tp_as_number set, but I couldn't track down
*where* it is being assigned; somewhere in ExtensionClass' setup, I
think.

(We have the same problem in IndexedCatalog, with our _ICPersistent
ExtensionClass that derives from Persistent.)

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