metaclasses and Exceptions

[Michael Hudson]

python at rcn.com (Raymond Hettinger) writes:

> Michael Hudson <mwh at python.net> wrote > One of the areas where PyPy is
> different from CPython is that there
> > are no old-style classes or instances, so exceptions are necessarily
> > new-style.  This has caused no real problems on any Python program
> > we've tried it on yet...
> 
> How does PyPy distinguish between instance and class arguments to
> raise?

"isinstance(x, type)", iirc.

The code is in this file:

http://codespeak.net/svn/pypy/trunk/src/pypy/interpreter/pyframe.py

in the function app_normalize_exception().  There's a kind of horrible
issue if you do things like:

class Nasty(type, Exception):
    pass

raise Nasty()

I can't remember what PyPy does here (the answer is quite possibly
"break").

> Given:  raise X
> Does it pass X or X()?

Depends on X!  Has to, really, or we certainly would have had more
problems from this than we've had.

Cheers,
mwh

-- 
  "declare"?  my bogometer indicates that you're really programming
  in some other language and trying to force Common Lisp into your
  mindset.  this won't work.            -- Erik Naggum, comp.lang.lisp