Move to Python3

[junghans]

https://pythonclock.org/

[jkrajniak]

Question regarding this task (rather decision for product owner); do we plan to still support Python 2.x if we migrate the code base to Python 3.x ?

[junghans]

Fedora 30 doesn't include h5py (and other packages) for python2 anyhow, so we have to start moving on this!

[stuehn]

Supporting python2 and python3 at the same time would in principle be possible. But due to limited manpower I would opt to drop python2 support completely. Since moving to python3 will render many existing espressopp scripts non-working we have to provide some kind of upgrade path for old user-scripts as well. ESPResSo++ 3.0 would be a nice version number for python3 support ;-)

[junghans]

2to3 with a bunch to tweaks?

[jkrajniak]

I suppose, on branch py3 I have already done the basic conversion with 2to3. It compiles, however there is an issue with abstract classes which are not compatible with py3. Also, I am not entirely sure that PMI itself can work with py3.

[junghans]

@olenz do you have a PMI for python3?

[mcepl]

2to3 with a bunch to tweaks?

It is a way not enough: as a person who ported another large project (with C extensions; M2Crypto) to be dual py2k/py3k, I can tell you that 2to3 just doesn't even start to cover what’s the most complicated: dealing with different versions of strings.

Some documentation on the topc:

• https://docs.python.org/3/howto/pyporting.html and https://docs.python.org/3/howto/cporting.html are pretty good introduction
• https://matej.ceplovi.cz/clanky/PyCon18-m2crypto/ presentation I had on the topic on PyConCZ'18
• http://python-future.org/compatible_idioms.html is pretty nice as well

[junghans]

Time is nearly up....

[junghans]

And the time is up!

[junghans]

https://bugs.gentoo.org/713568

[junghans]

gentoo/gentoo@3f27a55