[Python-ideas] IP addressing library, aka reviving PEP 3144 (Re: Add from __experimental__ import bla)

[Nick Coghlan]

On Fri, Sep 2, 2011 at 8:03 AM, Peter Moody <pmoody at google.com> wrote:
> I'll make an implementation with these changes this weekend.

Great to hear!

> It sounds like it's going to be clunky, but that's definitely with a grain or two of bias.

Hopefully it won't be too inconvenient - in theory, it just means that
when you derive the network details from a host address and masking
information you can't throw the original host address information away
any more (since IPNetwork own't be keeping it around).

> Documentation isn't my strong suit, but assuming the implementation is
> palatable to all involved, that can be forthcoming as well.

Splitting the API up a little should actually make the documentation
task itself easier. For folks that are already familiar with
networking concepts, it isn't that hard to mentally map the
"IPNetwork" name as meaning "either an actual IP network or else an
arbitrary host/netmask pair". We might grumble about it (*cough*), but
we wouldn't be confused once we made the connection.

However, once ipaddr goes into the standard library, its module
documentation is going to be the first introduction many future Python
programmers will have to the details of how IP addressing actually
works. We'll refer them off to other resources, of course, but having
clean semantics in the API itself is important in helping people that
are *not* already networking experts use the module correctly. That
means having the class model map cleanly to the real world entities it
represents, and while IP networks and specific interfaces on those
networks are both represented accurately by the combination of an IP
address with masking information, they're *not* the same kind of
thing.

It's the difference between using Pair(a, b) for both 2-D coordinates
and rational numbers vs using separate Point(x, y) and Rational(n, d)
classes. Yes, the information stored in both cases is the same, but
the semantics assigned to that information changes.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia