smtplib problem with newly rebuilt Debian/lenny system

[cassiope]

A hard drive failure forced me to rebuild my main system.  Just a few
things haven't been restored; one of them is a python script which is
used to email users of important events.

In attempting to diagnose the cause, I tried directly executing the
lines inside the python2.5 interpreter:

        import  smtplib
        s= smtplib.SMTP('localhost')

but the second line causes  a traceback:

        File "<stdin>", line 1, in <module>
        File "/usr/lib/python2.5/smtplib.py", line 244, in __init__
            (code, msg) = self.connect(host, port)
        File "/usr/lib/python2.5/smtplib.py", line 310, in connect
            raise socket.error, msg
        socket.error: (97, 'Address family not supported by protocol')

This is with exim4 and python2.5 on a newly installed lenny system.
No error messages appear in /var/log or /var/log/exim4 directories.

Helpful clues or pointers to relevant documentation would be
appreciated!

        -f