Re: [gentoo-dev] Stabilization of Python 3.1

[Arfrever Frehtes Taifersar Arahesis]

2009-09-20 19:47:28 Nirbheek Chauhan napisał(a):
> On Sun, Sep 20, 2009 at 11:05 PM, Arfrever Frehtes Taifersar Arahesis
> <Arfrever@g.o> wrote:
> >> Package X (stable) requires python-2
> >> Package Y (stable) requires python-3
> >>
> >> => User can't use both at the same time.
> >
> > Distribute/Setuptools will ensure that appropriate shebang is present in Python
> > scripts. In other cases, we can easily modify shebangs in installed scripts.
> > (A new function in python.eclass could be created for this purpose, but until
> > now it isn't needed.)
> >
>
> Oooh, this will lead to more phun!
>
> Package A (module, stable) requires python-3
>
> However, A is a dependency of *both* X and Y
>
> Now what? Slotting? Install to both/all python prefixes? Or some other
> ugly solution?

There is a difference between Python scripts and Python modules.

Python scripts should have shebang and this shebang is used to decide
which interpreter should be used when './script.py' is called. But it
is possible to call Python scripts using 'pythonX.Y script.py' which
will enforce using of pythonX.Y instead of interpreter specified in
shebang in this script. When one Python script executes another Python
script (using e.g. subprocess.Popen()) then both scripts will work
correctly even when they have different shebangs.

Python modules shouldn't have shebang. Python modules are intended to
be imported from Python scripts or other Python modules. Any shebang
in a Python module is ignored, when this module is imported using 'import'
statement.

The chance that well known and often used Python modules start
unconditionally require Python 3 in the near future is small, but
Python scripts can safely do it.

For example PyQt4 supports both Python 2 and 3, but a useful script, which
uses PyQt4, might require Python 3.

> Seriously, if you *really* *really* want python-3 stable, it should:
>
> 1) NOT show up in `eselect python` to set as the default interpreter

When a user wants to work for an hour with a script requiring Python 3,
and doesn't want to use e.g. Portage during this time, then it is
reasonable to run 'eselect python set python3.1' once and be able
to just use './script.py' instead of having to type 'python3.1 script.py'
every time. Next this user can switch active Python back to 2.6.

> 2) NOT be a dependency of any package in stable

It isn't implementable without having to change dependencies in hundreds
of packages. There is nothing wrong in having Python 3 installed which
would use small amount of disk space.

-- 
Arfrever Frehtes Taifersar Arahesis