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To: python-list@python.org
From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: Order of addresses returned by socket.gethostbyname_ex()
Date: Mon, 22 Aug 2011 13:34:57 -0400
References: <356978ef-e9c1-48fd-bb87-849fe8e27a79@p5g2000vbl.googlegroups.com> <roy-44FF9C.07265622082011@news.panix.com> <034ff4bf-e3e4-47ff-9a6c-195412431e73@s20g2000yql.googlegroups.com>
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On 8/22/2011 7:39 AM, Tomas Lid=C3=A9n wrote:
> On 22 Aug, 13:26, Roy Smith<r...@panix.com>  wrote:
>> In article
>> <356978ef-e9c1-48fd-bb87-849fe8e27...@p5g2000vbl.googlegroups.com>,
>>   Tomas Lid=C3=A9n<to...@liden-privat.net>  wrote:
>>
>>> In what order are the addresses returned by socket.gethostbyname_ex()=
?
>>
>>> We know that gethostbyname() is indeterministic but hope that
>>> gethostbyname_ex() has a specified order.
>>
>> Why would you hope that?  Or maybe a better question is, why would you=

>> expect that?  In general, all name resolution calls return results in
>> arbitrary order.  In some cases, results are intentionally changed on
>> every call (i.e. round-robin) in an attempt at load sharing.
>>
>> What kind of ordering were you hoping for?
>
> See previous posts.
>
> Basically I was asking about the contract for this method..

The doc "Return a triple (hostname, aliaslist, ipaddrlist) where=20
hostname is the primary host name responding to the given ip_address,=20
aliaslist is a (possibly empty) list of alternative host names for the=20
same address, and ipaddrlist is a list of IPv4/v6 addresses for the same =

interface on the same host (most likely containing only a single address)=
=2E"

> hoping that it is deterministic.

As far as I can see, that is not in the contract.

> Our testing indicated that the interfaces are returned in a specific
> order, but we want to know if this is really the case (on all
> platforms).

Even if it were so now, a patch could change things.

--=20
Terry Jan Reedy