Update setting of dlopenflags() to current Python standards (fixes #632)

[heplesser]

This solves Python 3.6 compatibility problems (#632) and removes code deprecated since Python 2.6.

[heplesser]

@Silmathoron Could you test this with Python 3.6? I have only tested 3.5 and 2.7 on OSX, while Travis will test 2.7 under Linux.

[heplesser]

Hm, seems that at least Ubuntu 14.04 does not provide RTLD_NOW in ctypes, and that importing pynestkernel fails if it is not set. So we may need to import DLFCN. I will update the PR tomorrow.

[Silmathoron]

All good under 3.6 also 👍

[heplesser]

@Silmathoron I just (about five minutes ago) pushed some fixes. Is your 3.6 approval with those fixes, or was that based on my push from about 15 hours ago?

[Silmathoron]

Yes, don't worry ;)

[DimitriPlotnikov]

Dear @Silmathoron and @heplesser,

I have been working quite a bit on the PR and corresponding issue. Now, I'm a bit confused what is the actual problem been solved in there.

I'll explain what did I try. In a clean Ubuntu 16.4.1LTS with python 2.7 and 3.5 I tried:

Building nest with python3 flags (-Dwith-python=3)
nest-simulator-master: python2 doesn't work with nest. python3 interpreter works with nest.
nest-simulator-PR: python2 doesn't work with nest. python3 interpreter works with nest.

Building nest without python 3 flags (-Dwith-python=3)
nest-simulator-master: python2 works with nest. python3 doesn't work with nest (problem mentioned in the issue).
nest-simulator-PR: python2 works with nest. python3 works with nest.

In my opinion It would be helpful to complement the issue with the information about:
a) Which software version were used
b) How nest-simulator were build
c) How to reproduce the error

[Silmathoron]

Hi @DimitriPlotnikov!
Unfortunately I'm a bit unsure about what your problem is (and I think there are unfortunate copy-paste in your comment ^^")

Just to make sure everything is clear:

• using -Dwith-python=X will install PyNEST for python X.Y (with highest available Y) only, e.g. -Dwith-python=2 will most probably install it in the path of python 2.7, meaning that any python 3.Y on your machine won't be able to use it (and the reverse is true if you use -Dwith-python=3
• the actual problem with the previous __init__.py was that, for python 3.6 (i.e. installing with -Dwith-python=3 and python 3.6 available on your machine), the import failed.

Thus, HEP's changes make sure that this problem is corrected:

1. sys.setdlopenflags(os.RTLD_NOW | os.RTLD_GLOBAL) works from 3.3 on
2. sys.setdlopenflags(dl.RTLD_GLOBAL | dl.RTLD_NOW) should work for 2.6--3.2 on most platforms
3. if not, one of sys.setdlopenflags(DLFCN.RTLD_GLOBAL | DLFCN.RTLD_NOW) or sys.setdlopenflags(ctypes.RTLD_GLOBAL | ctypes.RTLD_NOW) should do the trick
4. unless we're on a mac, then we need sys.setdlopenflags(ctypes.RTLD_GLOBAL)

[DimitriPlotnikov]

@Silmathoron

You provided me the information which I more or less wanted to know. I'll conduct a test with python 3.6

And no, there is no copy&paste errors in my previous message. I just summarized my observations and tests which I done.

[Silmathoron]

Building nest without python 3 flags (-Dwith-python=3)

Looks highly suspect to me, though... but ok, let us know ;)

[DimitriPlotnikov]

From: https://github.com/nest/nest-simulator/blob/master/INSTALL

-Dwith-python=[OFF|ON|2|3]                   Build PyNEST. To set a specific Python version, set 2 or 3. [default=ON]

Since there is no information regarding such options in the PR and issue I tried to reconstruct it from the docu. If I did it wrong, please, let me known.

[Silmathoron]

Sorry, I should have made it clearer: I just meant I think you used 3 when you wanted to use 2.
I would expect

Building nest without python 3 flags (-Dwith-python=2)

But as I said, I think it's a copy-paste error since you seem to understand the option without any problem ;)

[heplesser]

@DimitriPlotnikov Did your test with Python 3.6 go well?

[DimitriPlotnikov]

@heplesser
I'm still actively testing the PR in different configurations. Update the PR and issue today during the day.

[DimitriPlotnikov]

Tested the PR in a Ubuntu 16.10 instance with following python version: 2.7.12, 3.5, 3.6. I was always able to import nest in every of the mentioned python interpreters.

[heplesser]

Summary: NEST now works with Python 3.6.