[petsc-dev] #!/usr/bin/env python2?

[Toby D. Young]

Greetings Jed,

I ran into the python2/python3 problem a couple of months back on my
gentoo box. Since I found no comfortable way to switch to python3, I
switched my default python back to 2 (but that does not answer your
question).

> Since PETSc's use of Python does not work with python3, I think it makes
> sense to put
>
> #!/usr/bin/env python2
>
> in all the python files.  Is there any reason not to do this?

I wonder if a simpler approach would be to start the PETSc configure with
a check on the python version? That way one can edit a single file rather
than many and would make future compatibility/development/migration to
python3 easier. It should be possible to check for the existance of
python2 on the system and if so use that as a default.

Something like:

if (python -V gives major number >= 3)
   check for python2
      if (no python2 exists)
         panic and/or vomit on the petsc-user
      else
         use python2
else
   (do nothing, use python major number <= 3)

Thankfully getting the version number out of python is still the same. I
get this from my gentoo box where both are installed but I fixed python2
to be the favourite (default).

tyoung at wiatr ~ $ python -V
Python 2.6.5
tyoung at wiatr ~ $ python2 -V
Python 2.6.5
tyoung at wiatr ~ $ python3 -V
Python 3.1.2

The check could be done right at the top of configure. I'm not much of a
python writer, but I could try to hack something like that together if
this is a reasonable way forward. There may be even simpler ways of doing
the same thing... I would be happy to try it out for us.

Does that make sense? What do you think?

Best,
	Toby


-----

Toby D. Young
Assistant Professor

Institute of Fundamental Technological Problems
Polish Academy of Sciences
ul Adolfa Pawinskiego 5b
02-106 Warsaw
Poland

www:   http://www.ippt.gov.pl/~tyoung
skype: stenografia