This tip is in the docstring for the CherryPyWSGIServer class, in gluon/wsgiserver.py :
bind_addr: The interface on which to listen for connections.
For TCP sockets, a (host, port) tuple. Host values may be any IPv4
or IPv6 address, or any valid hostname. The string 'localhost' is a
synonym for '127.0.0.1' (or '::1', if your hosts file prefers IPv6).
The string '0.0.0.0' is a special IPv4 entry meaning "any active
interface" (INADDR_ANY), and '::' is the similar IN6ADDR_ANY for
IPv6. The empty string or None are not allowed.