>> 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. >> 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-) >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). >> 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. 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
