I think I understand. This simple code does not compile with python 3.0:

def f():
    e = None
    def g():
        e

    try:
        pass
    except Exception as e:
        pass # SyntaxError here???

The reason is that since 3.0, a "del e" statement is generated by the
compiler (see http://www.python.org/dev/peps/pep-3110/#semantic-changes)
and this conflicts with the first block of the function.

This issue is much more complicated than it seemed...
A solution could be to generate "e=None" instead of "del e".