On Mon, 28 Sep 2009 at 22:11, "Martin v. L??wis" wrote:
Martin v. L??wis <martin <at> v.loewis.de> writes:
Could you explain what benefit there is for allowing the user to create
network objects that don't represent networks? Is there a use-case
where these networks-that-aren't-networks are something other than a
typo? Under what circumstances would I want to specify a network as
192.168.1.1/24 instead of 192.168.1.0/24?
[...]
So Python code has to make the computation, and it seems most natural
that the IP library is the piece of code that is able to compute a
network out of that input.
The thing is, it doesn't create a network, it creates a hybrid "network plus
host" which retains knowledge about the original host (that is, 192.168.1.1
rather than simply 192.168.1.0, if you enter "192.168.1.1/24").
That's what the OP meant with "networks-that-aren't-networks", and that's what
people are objecting to.
That's not the question that was asked, though - the question asked
was "Under what circumstances would I want to specify...". I hope
most people agree that it is desirable to be able to specify a network
not just by its network address.
But then it's not a network, it is an ipaddress-plus-mask. It is exactly
that conflation that we are objecting to. There is no question about
the use case of _specifying_ a network ip plus a netmask and deriving
a network object from that. That is unquestionably required by any
useful API. The argument is about whether the object returned is a
Network object, or a hybrid object representing _both_ an IP address
and a network. It is the latter, which ipaddr does, which many of us
find problematic and likely to lead to hard to read programs that will
probably produce maintenance errors.
I observe that this line in the current PEP rationale:
IP addresses and IP networks are distinct.
is not in fact achieved by the reference implementation. Peter, however,
clearly thinks it is, since it is listed as a design goal of ipaddr.
This is a language disconnect I don't understand, which I think has
been the source of a lot of the difficulties in this thread.
--David_______________________________________________
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