class with invalid base class

[Michael Hudson]

Thomas Heller <theller at python.net> writes:

> "Andrew Dalke" <adalke at mindspring.com> writes:
> 
> > Out of curiosity, I tried passing using an invalid base
> > for a class.  I can't explain why I got the error messages
> > I did.  Can someone here enlighten me?
> >
> >    # Here I'm just curious
> >
> >>>> def spam(a, b):
> > ...  return a+b
> > ...
> >>>> class Spam(spam):
> > ...  pass
> > ...
> > Traceback (most recent call last):
> >   File "<interactive input>", line 1, in ?
> > TypeError: function() argument 1 must be code, not str
> >>>>
> >
> >   # What's 'function'?  Why is it called?
> 
> It's the Don Beaudry hook ;-).  If the base class has callable a
> __class__ attribute, this is called with three arguments: The name of
> the new class, a tuple of the bases, and a dictionary.  Or something like
> this, the details may be wrong...

Actually, I think it's type(baseclass) that gets called -- otherwise
you wouldn't be able to inherit from old-style classes!  What's
changed since 2.2 is that type objects are now callable.

(Isn't it amazing how something as simple as metaclasses -- and they
*are* a simple idea -- can be *so* confusing?  I wrote and rewrote
that paragraph at least three times...)

Cheers,
mwh

-- 
  But since your post didn't lay out your assumptions, your goals,
  or how you view language characteristics as fitting in with 
  either, you're not a *natural* candidate for embracing Design by 
  Contract <0.6 wink>.    -- Tim Peters, giving Eiffel adoption advice