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Re: dependancies issues




On 2018-03-28 at 16:50, Abdullah Ramazanoglu wrote:

> On Wed, 28 Mar 2018 09:46:53 -0400 The Wanderer said:
> 
>> On 2018-03-28 at 09:39, Laurent Debian wrote:
>> 
>>> Dear all, I have one question Does that aptitude message looks
>>> normal to you :"
>>> 
>>> "python-tornado breaks : python-zmq (< 17) but 16.0.2-2+b1 is to
>>> be installed"
>>> 
>>> Does I misunderstand or does it looks like aptitude thinks that 
>>> 16.0... is not less than 17 ?
>> 
>> No, it's saying "because the version of python-zmq which is
>> selected for installation is 16.x, we can't install a version of 
>> python-tornado which says it only works with version 17 and
>> above".
>> 
>> Why version 16.x is selected for installation is another question,
>> but we don't have enough information to go on in that regard.
> 
> Sorry but I still don't get it. As I understand, aptitude appears to 
> say that python-zmq with version *less than* 17 is needed?

No.

The relationship "Breaks: packagename < X" means that any version of
'packagename' which is less than version X will not work with this
package. (Here, "packagename" = "python-zmq" and "X" = "17".)

A "Breaks" is not a "Depends"; it's more closely akin to a "Conflicts",
which is basically the opposite of a "Depends".

Michael Lange's reply summarizes this accurately.

> That aside, python-tornado and python-zmq neither depends nor
> conflicts with one another. It may be different for Stretch, though.

As a side note, "Conflicts" and "Breaks" are both defined relationships
for the apt package database, and they have different meanings. I don't
remember offhand which meanings attach to which term, though.

<snip>

> So, where exactly python-zmq enters the picture, I don't know.

Trying to figure that out would lead us back to the question: what
exactly was the command which resulted in the original message you
quoted?

At a glance, I wouldn't expect that that message could ever appear
unless a version of python-tornado which does have a Breaks: against
'python-zmq < 17' is being considered for installation.

-- 
   The Wanderer

The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore all
progress depends on the unreasonable man.         -- George Bernard Shaw

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