[ZODB-Dev] new-style 2.2 classes and ZODB?

[Kendall Clark]

Folks,

I guess I just assumed that "ZODB works with 2.2" meant that you could
write persistent new-style classes, but maybe that's not the case?

Earlier, while trying to kill time, hoping a fix for the ZODB segfault
I'm getting is found, I tried to write a very simple persistent
new-style class.

The first thing I did was:

class Foo(object, Persistent):
    pass

which gets a

TypeError: metatype conflict among bases

Okay, I think, I don't really grok the new multi-inheritance
algorithm, but perhaps I should switch those around:

class Foo(Persistent, object):
    pass

Bingo, no more TypeError -- I'll have to figure out why this matters
at some point, but let's move on.

Now, let's add one simple get/set attribute to the class and try to
persist it. So I take the exemplar class from Guido's Unifying Types
and Classes paper:

class C(Persistent, object):
    
    def __init__(self):
        self.__x = 0
        
    def getx(self):
        return self.__x
        
    def setx(self, x):
        if x < 0: x = 0
        self.__x = x

    x = property(getx, setx)

if __name__ == "__main__":

    a = C()
    a.x = 10
    print a.x

Running "python2 C.py" gives this:

cmpu:~/forum$ python2 C.py
Traceback (most recent call last):
  File "C.py", line 22, in ?
    a = C()
  File "C.py", line 9, in __init__
    self.__x = 0
TypeError: function takes exactly 2 arguments (1 given)

Hmm, I have no idea what that's about, maybe there's something about
new-style classes I don't get yet... <read for 20 minutes; play around
with just about every __slots__, descriptors, property, staticmethod,
classmethod combo I can think of...>

Still no luck.

So, I think, forget about persisting *new* classes, how about:

class C(Persistent):
...

Does that work? Yes, just as you'd expect:

cmpu:~/forum$ python2 C.py
10

What about a non-persistent new-style class?

Yes, that works too:

cmpu:~/forum$ python2 C.py
10

Either I'm missing something really obvious, or Guido's exemplar class
doesn't like ZODB, or ZODB doesn't like it. Or maybe I read too much
into the statement that Standalone ZODB works with Python 2.2?

Any light that can be shed is appreciated.

Kendall Clark
--
Jazz is only what you are. -- Louis Armstrong