Classes as objects

[Ken Seehof]

"Daniel Klein" <DanielK at jBASE.com> wrote:
> Haven't posted for a while but I this time I am requesting some
assistence.
>
> I'm putting on a presentation on the benefits of Python over Java and one
of
> the points I would like to make is how everything is an object, even
> Classes. Can anyone out there in PythonVille provide a simple (practical)
> example of how classes can be used as objects?
>
> Thanks,
> Daniel Klein

Here's a debugging hack that messes with classes:

class Eyeball:
    def __setattr__(self, a, v):
        k = self.__class__.__bases__[1]
        print "<%s: %s = %s>" % (k.__name__, a, `v`)
        if hasattr(k, '__setattr__'):
            k.__setattr__(self, a, v)
        else:
            self.__dict__[a] = v

def watch(x):
    class E: pass
    E.__bases__ = (Eyeball, x.__class__)
    E.__name__  = 'Eyeball_%s' % x.__class__.__name__
    x.__class__ = E

def unwatch(x):
    try:
        e,k = x.__class__.__bases__
    except:
        e=None

    if e!=Eyeball:
        raise TypeError, 'not a watched instance'

    x.__class__ = k


>>> class Q:
...  pass
...
>>> q = Q()
>>> q.spam = 12
>>> watch(q)
>>> q.spam = 23
<Q: spam = 23>
>>> unwatch(q)
>>> q.qpam = 34
>>>

Of course, this can get much more fancy.  For example, I have
a version that writes all method calls on any instance object to
a log file.

- Ken Seehof kseehof at neuralintegrator.com