[Python-Dev] PEP 3144: IP Address Manipulation Library for the Python Standard Library

[Peter Moody]

On Wed, Aug 19, 2009 at 9:21 AM, R. David Murray<rdmurray at bitdance.com> wrote:
> On Wed, 19 Aug 2009 at 08:19, Peter Moody wrote:
>>
>> On Wed, Aug 19, 2009 at 6:47 AM, Tino Wildenhain<tino at wildenhain.de>
>> wrote:
>>>>
>>>> Le Tue, 18 Aug 2009 13:00:06 -0700, Peter Moody a écrit :
>>>
>>>>>> o.broadcast
>>>
>>>    IPv4Address('1.1.1.255')
>>>
>>> this is often used but not the only valid broadcast address,
>>> in fact, any address between network address and max(address with given
>>> netmask) can be defined as broadcast. Maybe biggest or greatest
>>> would be better name for the attribute. User is then free to interpret
>>> it as broadcast if desired.
>>>
>>> The attribute network returned as address object also does not seem
>>> right.
>>
>> by convention, the highest address in a given network is called the
>> broadcast address while the lowest address is called the network
>> address. They're also distinct addresses, as opposed to networks,
>> hence .broadcast/.network/etc returning IPvXAddress objects. calling
>> them .biggest and .smallest would be confusing.
>>
>> am I misinterpreting what you mean?
>
> Possibly.  Tino means exactly what he said:  the broadcast address
> does not _have_ to be the last IP, nor does the last IP _have_ to be
> a broadcast, though in practice they almost always are (and using the
> last IP as a host IP almost never works in practice in a heterogeneous
> network).  Check out the 'broadcast' option of the ifconfig command for
> confirmation that the broadcast address can be any IP in the network.
> Of course, for that to work all hosts on the network have to agree on
> what the broadcast is, hence the normal convention that the broadcast
> is the last IP in the network.
>
> As for the 'network' attribute, if you call it 'network' IMO it should
> be a network data type, which would make it rather redundant.  What you
> are actually returning is what I have normally heard called either the
> 'zero' of the network, or the "network number" or "network identifier";
> but never just "network" (a network has to have at least an implicit
> netmask to be meaningful, IMO).
>
> Since you are dealing with networks as a list of addresses, perhaps
> you should drop the 'network' attribute, make the 'broadcast' attribute
> settable with a default equal to self[-1], and let the user refer to
> the zero element to get the zero of the network if they want it.

making the broadcast address settable (with a default to self[-1])
might be reasonable, though it is different from just about every
other python implementation I've seen (IPy, ipv4.py, netaddr).

I'm not sure I understand your point about the network attribute.
what I'm returning with network is the subnet-id/base address of the
given network. Again, .network seems to be fairly standard for naming.

> --David