Improve Python version check for enum34 install

[ajoubertza]

Older versions of distutils don't handle the extended version dependency syntax. E.g. default packages on Ubuntu 14.04 fail, while Ubuntu 16.04 works. Use the sys module's version instead.

Failures look like this when trying to build a Debian package:

error in pytango setup command: 'install_requires' must be a string or list of strings containing valid project/version requirement specifiers
E: pybuild pybuild:256: clean: plugin distutils failed with: exit code=1: python2.7 setup.py clean 
dh_auto_clean: pybuild --clean -i python{version} -p 2.7 --dir . returned exit code 13

[ajoubertza]

Any reviewers keen to have a look at this minor change? Please 🙂

[vxgmichel]

I'm a bit confused about this issue, because setup.py is supposed to use setuptools and not distutils. What happens if one runs a simple python setup.py install on ubuntu 14?

[ajoubertza]

@vxgmichel It seems to work and starts compiling the C code (still running). The error happens when trying to build a Debian package - we're using a slightly modified version of the official one: https://salsa.debian.org/science-team/pytango/tree/master/debian, targeting Ubuntu 14.04.
Maybe it is caused by pybuild?

[vxgmichel]

What about python setup.py clean then?

[ajoubertza]

@vxgmichel Running python setup.py clean works fine too (sorry for the delay).

[jairomoldes]

I don't see any problem. Seems like "sys.version_info" is a safe and portable way of checking python version.

[tiagocoutinho]

I think the issue is that ubuntu 14.04 system packages are python 2.7.6 and setuptools 3.3.
Declaring platform specific dependencies feature only appeared in a more recent version of setuptools.

So far the only statement we have in PyTango is that we require python >= 2.7. Since we don't say anything about a minimum version of setuptools I am inclined to accept this PR unless anyone has any objection.

[ajoubertza]

Thanks for reviews @tiagocoutinho and @jairomoldes.