On Wed, Sep 16, 2009 at 8:21 PM, Andrew McNamara <andr...@object-craft.com.au> wrote: >>> I think we're in a painful middle ground now - we should either go back >>> to the idea of a single class (per protocol), or make the distinctions >>> clear (networks are containers and addresses are singletons). >>> >>> Personally, I think I would be happy with a single class (but I suspect >>> that's just my laziness speaking). However, I think the structure and >>> discipline of three classes (per protocol) may actually make the concepts >>> easier to understand for non-experts. >> >>I think this is where we disagree. I don't think the added complexity >>does make it any easier to understand. > > I argue that we're not actually adding any complexity: yes, we add > a class (per protocol), but we then merely relocate functionality to > clarify the intended use of the classes.
And I argue the moving this functionality to new classes (and adding new restrictions to existing classes) doesn't buy anything in the way of overall functionality of the module or a developer's ability to comprehend intended uses. >>> A particular case in point - if you want to represent a single IP address >>> with netmask (say an interface), you use a Network class, not an Address >>> class. And the .network attribute returns a Address class! >> >>Right, and I don't see where the confusion lies. > > I suggest you are too close to the implementation to be surprised by it. 8-) touche :) >>You have an address + netmask. ergo, you have a Network object. > > In a common use case, however, this instance will not represent a > network at all, but an address. It will have container-like behaviour, > but it should not (this is a property of networks, not addresses). So > the instance will be misnamed and have behaviours that are, at best, > misleading. > >>The single address that defines the base address (most commonly referred >>to as the network address) is an Address object. there is no netmask >>associated with that single address, ergo, it's an Address object. > > I would argue that a Network never has a single address - by definition, > it has two or more nodes. A .network attribute should return a Network > instance. If you want the base address, this probably should be called > .base_address or just .address (to parallel the .netmask attribute). .network is shorthand for network address. are .network_address and .broadcast_address less confusing? I have to say, though, .network/.broadcast are fairly common (IPy uses .net, netaddr and ipv4 use, IIRC .network...) >>> The reason I suggest having the Network class assert that masked bits be >>> zero is two-fold: >>> >>> * it ensures the correct class is being used for the job >>> * it ensures application-user errors are detected as early as possible >>> >>> I also suggest the AddressWithMask classes not have any network/container >>> behaviours for a similar reason. If the developer needs these, the >>> .network attribute is only a lookup away. >> >>the problem I have with this approach is that it seems like a long way >>to go for a shortcut (of checking if addr.ip != addr.network: raise >>Error). > > This isn't about shortcuts, but about correctness... having the Network > object represent a network, and having Address objects represent > end-points, and having errors discovered as early as possible. Then what I don't see is the purpose of your network-only-network-object. essentially identical functionality can be obtained with the module as is w/o the added complexity of new classes. Cheers, /peter > What I'm arguing here is that singletons should not simultaneously be > containers - it's not pythonic, and it leads to ambiguity. The underlying > IP concepts don't require it either: an IP address is a singleton, a > network is a container, and there is no overlap. Yes, an address may be a > member of a network, and having a reference to that network on the address > object is valuable, but the address should not behave like a network. > > -- > Andrew McNamara, Senior Developer, Object Craft > http://www.object-craft.com.au/ > _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
