[Python-Dev] Accept just PEP-0426

Glenn Linderman v+python at g.nevcal.com
Tue Nov 20 22:07:52 CET 2012

On 11/20/2012 12:46 PM, PJ Eby wrote:
> On Tue, Nov 20, 2012 at 11:49 AM, Vinay Sajip <vinay_sajip at yahoo.co.uk 
> <mailto:vinay_sajip at yahoo.co.uk>> wrote:
>     Also: what happens when a requirement is for setuptools (>= X.Y),
>     but the
>     distribute fork hasn't kept pace, and so only supports setuptools
>     at a lower
>     version than X.Y? I take it we're entirely comfortable with installing
>     setuptools X.Y in that case? How would you ensure the right
>     setuptools is
>     always loaded, since presumably both are on sys.path?
> Egg-based tools don't have any problem with this, since they set 
> sys.path to include the eggs needed for the running program.  Other 
> tools will have to tell the user and let them work it out, e.g. by 
> using a different virtualenv.
> I personally don't think that forks claiming to "provide" something is 
> really a good thing to encourage; ISTM that saying a package 
> *conflicts* with another is more accurate, e.g. distribute 
> Conflicts-Dist setuptools.  I also think distributions should say they 
> are obsoleted, rather than allowing other distributions to obsolete them.

Obsolete distributions won't say they are obsoleted, unless they receive 
further maintenance. However, if the distribution is obsolete because 
the maintainer has lost interest, they won't receive further maintenance.

> That is, centralized packaging systems rely on a central authority to 
> resolve issues of who provides what and obsoletes what; there's an 
> implicit "x obsoletes y [by decree of semi-independent third-party z]".
> However, in Python package metadata, it's "x obsoletes y [by decree of 
> x]".  IMO, this should be reversed to, "Y is obsoleted by x [by decree 
> of y]", and "installing Y will conflict with X [by decree of X]", so 
> that in each case the scope of authority for the statement is clear.
> That is, in each case (conflict or obsolescence), the project's 
> developers are declaring under what conditions they will not be 
> supporting an installation.  In the case of obsolescence, the 
> developer is saying, "this is being phased out, you should use that 
> other thing instead".  In the case of forks, the developer is saying, 
> "If you install both versions, something's gonna break."
> Note that installation conflict is a more conservative claim anyway: a 
> conflict between forked "foobar" packages is permanent, in the sense 
> that it doesn't matter what versions of both packages you're 
> interested in: they both want to install a foobar/__init__.py.  (Of 
> course, installers can and should detect that condition automatically, 
> but not until they download the package first.)

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