[Python-Dev] PEP 3144 review. (original) (raw)

Andrew McNamara andrewm at object-craft.com.au
Fri Sep 18 02:57:41 CEST 2009

Conceptually, you sometimes need a bare address, and other times, you need an address with an associated network (host interface configs, router configs, etc). By AddressWithMask, I really mean AddressWithEnoughInformationToDeriveNetworkWhenNeeded. Conveniently, IPv4 and IPv6 addressing allows us to derive the network from the host address combined with the netmask - in other words, we don't have to attach a real Network object to Address objects until the user tries to access it, and then we derive it from the address and mask. To clarify: when you say "derive the network" are you talking about the network (which is a container) or the network address = hostaddress & netmask (which is not a container)? I think you're referring to the later.

I mean a Network object which is a container (which, by definition, has a network address + mask).

If there's need for address+netmask, does it need to be a separate class? Perhaps Address objects could simply have a netmask property, defaulting to None. If you need an "address with mask" object, you create an Address and set the mask:

addr = Address(...) addr.netmask = "255.255.255.0"

Greg Ewing suggested this yesterday - I'm neutral on whether it's done this way or as a separate class. The implementation may be somewhat cleaner if it's a separate class, however.

If you have a .network attribute on an address object, checking if an address is in the same network as another address becomes:

addra in addrb.network As the module stands, you write that as: addra in addrb I don't think the intent is as clear with the later. I would find the later completely unclear and disturbing -- how can one address contain another address?

Yes - that's how it works now, and I can only see it resulting in confusion and bugs for no advantage.

-- Andrew McNamara, Senior Developer, Object Craft http://www.object-craft.com.au/

More information about the Python-Dev mailing list