[dev] Debian packaging Python2 deprecation

[David Lamparter]

Hi all,


as I'm currently cleaning up the Debian packaging and trying to get it
shipped, I've been asked (on Debian channels) about the python2
dependencies that we still have in the package.

First of all, I've converted all of them to "python2 | python3"
dependencies.  Since PR#3074 [https://github.com/FRRouting/frr/pull/3074
"frr-reload.py: Python3 compatibility"], frr-reload.py should also be
working correctly on Py3.

However, even this is rather unwelcome in Debian, especially for "new"
packages.

Since all of our supported Debian-based targets (i.e. starting at Debian
8/jessie and Ubuntu 14.04) have python3, I don't see a good reason to
retain python2 in our Debian packaging.  If you see any such reasons,
please voice them now.

NB(1): this is only about the DEBIAN PACKAGING.  Everything in FRR,
including clippy, works with either python2 or python3 and will continue
to do so.  However, the Debian packages will just list python3 as a
dependency.

NB(2): as far as I know, Debian will stop shipping python2 in 2019.  I
don't know what exactly that implies (you can probably still install it
somehow.)

NB(3): https://python3statement.org/

NB(4): Python2 will be EOL on January 1st, 2020
[https://www.python.org/dev/peps/pep-0373/]

NB(5): the "frr-pythontools" package / frr-reload.py cannot ship with a
"2 or 3" dependency.  It needs to choose between python2 and python3 to
get the #! shebang correct.  This will absolutely be Python3; that's the
only viable choice from an integration perspective.

Cheers,


-David