> Consider applications that need to validate addresses (or networks,
> but not both) supplied as user input:
>
> address = ipaddr.IP(input)
>
> if isinstance(address, ipaddr.IPv4):
>    if address.prefixlen != 32:
>        raise TypeError("Expecting IP address, not network")
> elif isinstance(address, ipaddr.IPv6):
>    if address.prefixlen != 128:
>        raise TypeError("Expecting IP address, not network")

Support for this can be added (its too late for Python 3.1).  User
input validation is a good use case.  For now I suggest the simpler
code:

if '/' in input:
    raise TypeError("Expecting IP address")
address = ipaddr.IP(input)

Or for a more pedantic test prior to calling ipaddr.IP.

if re.match('^[0-9a-fA-F:.]+$', input):
    raise TypeError("Invalid characters in IP address")

Please file a feature request on bugs.python.org for this one if you
haven't already.  We could add optional parameter(s) to ipaddr.IP to
enable only accepting host addresses or network addresses in the
future.