[Python-Dev] PEP 3144 review.

[Peter Moody]

On Wed, Sep 16, 2009 at 6:32 PM, Andrew McNamara
<andrewm at object-craft.com.au> wrote:
>>This proposal actually leads to 6 entities (3 for IPv4 and 3 for IPv6).
>
> Yes, I know - I was just trying to keep to the point.
>
>>It's still unclear to me what is gained by pulling AddressWithMask
>>functionality out of the current network classes. It's easy enough for
>>the concerned developer who to check if the entered network address
>>does actually have all of its host bits set to zero. It is not my
>>experience that this behavior is desired so often that having the
>>network classes behave as they do now leads to a great deal of
>>confusion.
>
> 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.

> 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.  You have an address
+ netmask. ergo, you have a Network object.  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.

> 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).

Cheers,
/peter

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