[Zope-Perl] Exception traceback

[Gisle Aas]

Today I improved the handling of python exceptions that pass through
perl.  What happens on the language barriers now is:

  python called from perl

     Any exceptions from python are extracted with PyErr_Fetch()
     and packed up in a Python::Err object which is assigned to $@
     and then re-thrown as a perl exception.

  perl called from python

     If perl has an outstanding exception when we get back to python
     then we check if $@ is a Python::Err object and if so unpack it and
     restore python exception state with PyErr_Restore().

     If $@ is not a Python::Err object, then raise an python exception
     "perl.error" with the stringified $@ as the value.

This arrangement should make it possible for python exceptions to pass
through a layer of perl code unaltered.  The only problem is that the
perl code make no traces of itself in the traceback object, and from
studying the code Python/traceback.c it does not appear that python
could easily deal with foreign callframes/traceback objects without
some core python patching.  The question is if this will be worth it?

Example of current behaviour:

------------------------------------------------------->8------------

import perl

perl.eval("""

sub callback {
   my $obj = shift;
   my $meth = shift;
   return $obj->$meth(@_);
}

""")

class Foo:
        def foo(self, a):
                print "calling foo", a
                return 3/a
        pass

obj = Foo()

print perl.call("callback", obj, "foo", 3)
print perl.call("callback", obj, "foo", 4.0)
print perl.call("callback", obj, "foo", 0)

------------------------------------------------------->8------------

$ python callback.py 
calling foo 3
1
calling foo 4.0
0.75
calling foo 0
Traceback (most recent call last):
  File "callback.py", line 24, in ?
    print perl.call("callback", obj, "foo", 0)
  File "callback.py", line 17, in foo
    return 3/a
ZeroDivisionError: integer division or modulo

Regards,
Gisle