This client still works, but relying on a 3rd party service has downsides for reliability and performance reasons. I've started a new project called asnlookup to allow one to perform lookups locally or to operate a similar service on their own infrastructure. If autonomy and 160,000 queries/second interests you, check it out.
Perform lookups by ip address and return ASN, Country Code, and Netblock Owner::
>>> import socket
>>> ip = socket.gethostbyname("www.google.com")
>>> from cymruwhois import Client
>>> c=Client()
>>> r=c.lookup(ip)
>>> print r.asn
15169
>>> print r.owner
GOOGLE - Google Inc.
See http://packages.python.org/cymruwhois/ for full documentation.