[petsc-dev] Configure won't find python

[Satish Balay]

On Sat, 18 Apr 2020, Satish Balay via petsc-dev wrote:

> On Sat, 18 Apr 2020, Satish Balay via petsc-dev wrote:
> 
> > On Sat, 18 Apr 2020, Jed Brown wrote:
> > 
> > > Satish Balay <balay at mcs.anl.gov> writes:
> > > 
> > > > Sure - the initial premise of this thread [as I understood] was: /usr/bin/python is python2. On python3 only installs - there is no /usr/bin/python (for ex: jedbrown/mpich-ccache docker file) - so we need to fix this issue in configure.
> > > >
> > > > I'm guessing that most installs will have  /usr/bin/python as python2 or python3 - so missing /usr/bin/python is a smaller problem. Its not clear to me why this is missing in jedbrown/mpich-ccache - and how many OSes or distro will default to this mode.
> > > 
> > > On Debian and Ubuntu, /usr/bin/python is part of python2; it isn't created if you `apt install python3`.
> > 
> > Ok - that a large userbase.
> > 
> > So when python2 deprecated in debian - there won't be /usr/bin/python anymore?
> 
> Also - debian does alternatives - don't know if they can setup a default python [python2 vs python3] through this mechanism - and have anyone installed as default.
> 
> [for ex: I think if openmpi is installed /usr/bin/mpicc is automatically setup as default via /etc/alternatives. I don't know if the same happens for mpich]

With older OS versions - python2 is system default, python3 is the add-on. So there is no special support to make the add-on python3 the default. In such cases - some minimal installs can potentially exclude some system defaults - i.e system default python. Is this the case for jedbrown/mpich-ccache or - is it that newer versions of debian have 'python3' as system-default - but don't have /usr/bin/python [because this now part of the add-on python2 package?]

Satish