confusion around CustomException example in 'Python in a Nutshell'

[erick_bodine at comcast.net]

In Martinelli's Nutshell book in the Exceptions chapter there is an
example of a custom exception class (pg.112) that I am trying to
implement without success.  The custom exception class example pulls
sys.exc_info() into an attribute and I am assuming that the attribute
would then contain the raised exception info in a tuple (admittedly I
could be assuming erroneously).

class LinuxDriverError(Exception):
    def __init__(self, *args):
        Exception.__init__(self, *args)
        self.message = args[0]
        self.wrapped_exc = sys.exc_info()

try:
    raise LinuxDriverError, "raising Cain!"
except CustomException, error:
    print error.message
    print error.wrapped_exc

    # just checking
    print "sys.exc_info(): ", sys.exc_info()

If I run the above code I get the following output:

Just raising Cain!
wrapped_exc:  (None, None, None)
sys.exc_info():  (<class __main__.LinuxDriverError at 0xf6f774dc>,
<__main__.LinuxDriverError instance at 0xf6f74bec>, <traceback object
at 0xf6f7193c>)

I do not understand why the wrapped_exc attribute contains no objects.

I am running 2.3.4 on a fedora core 3 box.

thanks,

erick