Set python3 as interpreter for doc tools

[juliantaylor]

The scripts require python3 so the interpreter should use that.
python does not point to python3 on most distributions.

[josef-pkt]

@bashtage @thequackdaddy any comments?
I have no idea about this, and it is not relevant on windows where these are ignored, i.e. I don't care either way..

[coveralls]

Coverage increased (+0.02%) to 84.207% when pulling 1da0694 on juliantaylor:fix-interpreters into 34ae057 on statsmodels:master.

[bashtage]

I would probably reject this since python3 isn't necessarily available on all platforms. Essentially these should be run in a vurtual env with python 3.6+ as the default interpreter, in which case python is fine.

[juliantaylor]

python3 should be available on all platforms where this execution method is available, see the recommendations of https://www.python.org/dev/peps/pep-0394/

By using python for python3 scripts you are breaking all unix like distributions except arch (where python3 also exists).

virtualenv should also have python3 available if not that is a bug as it is violating the pep.

[josef-pkt]

related thread https://groups.google.com/forum/#!topic/comp.lang.python/YGwlPPxeVr8
I didn't really try to understand this because it is irrelevant for me, and I don't know much about the various Linux distributions.

[josef-pkt]

to clarify the doc build requirements.

Does the doc build now require python 3 or does it still work with python 2.7 also?

If the former, then the change looks useful to force python 3.
If it works with either version, then a plain python would be appropriate, and leave it to the system to select the appropriate version.

[juliantaylor]

it does not work in python2, the files use python3 features, e.g. futures or the encoding argument of open

[bashtage]

The expectation of this file, and the doc generation in general, is that it is run in an environment where python 3 is the default python.

[juliantaylor]

That assumption does not fit with pythons own pep. I do not see why statsmodels is different from all other python software in this regard that it must assume this non-standard behaviour.

[josef-pkt]

merged,
IMO it is better to be explicit about the python version when we don't follow our standard py2/3 compatibility.