[Python-Dev] PEP 3144 review. (original) (raw)

Scott Dial scott+python-dev at scottdial.com
Mon Sep 28 22:19:15 CEST 2009

Martin v. Löwis wrote:

Martin v. Löwis <martin 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.

I can't help but feel that you and many others jumping on Antoine et al. have skipped reading or only skimmed this topic of discussion.

Antoine Pitrou wrote:

We just need a factory function which returns a tuple after parsing:

>>> addr, net = parseaddresswithmask('192.168.1.1/24') >>> addr == IPv4Address('192.168.1.1') True >>> net == IPv4Network('192.168.1.0/24') True

I still back this suggestion. I would also support a "loose=True" flag for the IPNetwork constructor, which would allow host bits to be non-zero.

However, I will never support a proposal that includes retaining the host address. I believe I am not alone in that. However, Peter has made it quite clear that he will never change that about the IPNetwork classes.

I would be quite glad to not have ipaddr included in the stdlib. As I can only imagine code that uses it being quite confusing to maintain (e.g., "wait is that actually a network or is that someone using IPNetwork to be an IPAddressWithMask?").

-1.

-- Scott Dial scott at scottdial.com scodial at cs.indiana.edu

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