New+old-style multiple inheritance

[stephenpas at googlemail.com]

On Dec 18, 8:25 pm, Carl Banks <pavlovevide... at gmail.com> wrote:
> On Dec 18, 2:09 pm, Jonathan Gardner
>
>
>
> <jgardner.jonathangardner.... at gmail.com> wrote:
> > On Dec 18, 7:08 am, "stephen... at googlemail.com"
>
> > <stephen... at googlemail.com> wrote:
> > > We are trying to monkey-patch a third-party library that mixes new and
> > > old-style classes with multiple inheritance.  In so doing we have
> > > uncovered some unexpected behaviour:
>
> > <snip>
>
> > > I know this level of messing with python internals is a bit risky but
> > > I'm wondering why the above code doesn't work.
>
> > You've already discovered why--you're mixing old and new style
> > classes.
>
> > Monkey patching is definitely unpythonic. You must be a Ruby guy. Why
> > don't you try doing something else to get the behavior you want,
> > something more explicit?
>
> Time and place.
>
> A well-considered, timely monkey-patch can sometimes save all kinds of
> workarounds and other headaches.
>
> Carl Banks

Indeed, I chuckled at the idea I was a Ruby programmer.  Of course
it's a bit of a hack but monkey-patching has been common place in the
Zope world for years (maybe Zope3 has rid itself of the problem).

Agreed, mixing new and old-style classes in multiple inheritance is
asking for trouble (although the Guido's essay on the new-style
classes  suggests you can: http://www.python.org/download/releases/2.2.3/descrintro/#subclassing).
I won't name and shame the library involved but unfortunately we can't
always pick and choose the tools we work with unless we want to write
(or rewrite) everything ourselves.

Cheers,
Stephen.