[Python-ideas] Migration of /usr/bin/python to python3

[Ian Lee]

+1

An issue that I've noticed recently (I haven't had the time to fully track
this one down yet, but I suspect it's a setuptools issue) takes a "last one
wins" approach to scripts that get written into the same bin directory
(e.g. --user installs).

$ python2.7 -m pip install --user ipython
>
> $ head -n1 ~/.local/bin/ipython*
> ==> /home/ianlee1521/.local/bin/ipython <==
> #!/usr/bin/python2.7
>
> ==> /home/ianlee1521/.local/bin/ipython2 <==
> #!/usr/bin/python2.7
>
> $ python3.4 -m pip install --user ipython
>
> $ head -n1 ~/.local/bin/ipython*
> ==> /home/ianlee1521/.local/bin/ipython <==
> #!/usr/bin/python3.4
>
> ==> /home/ianlee1521/.local/bin/ipython2 <==
> #!/usr/bin/python2.7
>
> ==> /home/ianlee1521/.local/bin/ipython3 <==
> #!/usr/bin/python3.4


So the packages end up in the separate, versioned directories
(~/.local/lib/pythonX.Y/site-packages), but with the scripts ending up in
the same bin directory, the implicit script "~/.local/bin/ipython" ends up
changing to use the hashbang of the Python version which last installed the
package (see highlighted above).

I would expect that the implicit script ("~/.local/bin/ipython") should use
the implicit python version, e.g. "#!/usr/bin/python".

Alternatively, maybe I just shouldn't ever be installing user versions of
both Python 2 and Python 3 versions of a package.



~ Ian Lee

On Wed, Mar 11, 2015 at 1:38 PM, M.-A. Lemburg <mal at egenix.com> wrote:

> On 11.03.2015 21:03, David Mertz wrote:
> > https://www.python.org/dev/peps/pep-0394/
>
> I think the migration should start with modifying scripts to use
>
> #!/usr/bin/env python2
>
> when they are Python 2 only (*) and
>
> #!/usr/bin/env python3
>
> when they are Python 3 only and
>
> #!/usr/bin/env python
>
> only when they support both Python 2 and 3.
>
> "Explicit is better than implicit" and all that Zen :-)
>
> Once that's done, switching the symlink is really a no-brainer.
>
> The recipe for this is easy too:
>
> 1. replace all "#!/usr/bin/env python" with "#!/usr/bin/env python2"
> 2. migrate your scripts one by one to either Python 3.x or
>    to Python 2.7 + 3.4+
> 3. after migration replace "#!/usr/bin/env python2" with
>    "#!/usr/bin/env python3" or "#!/usr/bin/env python" resp.
>
> (*) Some OSes may require to use python2.7, if they don't come
> with a symlink from python2 -> python2.7.
>
> --
> Marc-Andre Lemburg
> eGenix.com
>
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