[petsc-dev] Configure won't find python

[Jacob Faibussowitsch]

> And what if someone is running on a (perhaps old) Linux distro that does not have python3 installed by default?

The idea would be to find both but prefer python3, but that’s infeasible inside configure without a separate pre-configure configure to write “configure.py" or virtual-env.

> for pyimpls in python3 python2 python /usr/bin/python /usr/bin/env python ; do
> command -v > /dev/null $pyimpls && exec $pyimpls $0 "$@“

> And there  you have, you are trying to check for '/usr/bin/env python', but the shell code you wrote will not work the way you are expecting.
> Also, unless you are running on a funny environment that does not have /usr/bin/ in $PATH, the trial for 'python' should be enough, and the /usr/bin/python /usr/bin/env python look redundant. Am I missing something?

This line checks if pyimpls exists in order, and then runs pyimpls ./configure so if any of the previous pyimpls exist then it doesn’t check the rest. The last “ should be a regular quotation mark. If it finds a working python it runs configure once then exits, instead of continuing through the rest of the list.

> "Echo" ? Are you really running this on Ubuntu? 

Auto-correct strikes again :(. It is “echo” in my script.

> BTW, Are you aware of the behavior of `command -v` with shell aliases?

No, this is a good point you bring up. I tried using the option -p from the manpage but that also doesn’t seem to skip aliases. Not sure how this can be addressed, seems like escaping pyimpls using \ or ‘ or “ doesn’t fix this either...

> -p    use a default value for PATH that is guaranteed to find all of
>             the standard utilities

To be clear I’m not saying my script is a change petsc should adopt, hence no MR. It is a hack and a half, and likely doesn’t work on some of the other shells as well as a whole host of portability problems. It's more-so to foster discussion, and see if anyone else has a cleaner automatic form.

Best regards,

Jacob Faibussowitsch
(Jacob Fai - booss - oh - vitch)
Cell: (312) 694-3391

> On Apr 17, 2020, at 4:21 PM, Lisandro Dalcin <dalcinl at gmail.com> wrote:
> 
> 
> 
> On Fri, 17 Apr 2020 at 20:41, Jacob Faibussowitsch <jacob.fai at gmail.com <mailto:jacob.fai at gmail.com>> wrote:
> Hello All,
> 
> I use an Ubuntu docker image based on jedbrown/mpich-ccache and ran into the following error (Dockerfile attached as well).
> 
> If in a user only has python3 installed and not python2 then /usr/bin/python doesn’t exist.
> 
> And what if someone is running on a (perhaps old) Linux distro that does not have python3 installed by default?
> 
> Given that python2 has gone the way of the dodo perhaps petsc should be looking for python3 over python2. This is a somewhat funky but functioning implementation that replaces the shebang line in configure that I have been using to default to python3. I don’t know how portable it is however, I believe “command" is not universally available in every shell?
> #!/bin/sh
> # “”” is comment in python, and : is noop in shell so this configure can be run as ./configure and python2.7 ./configure
> """:"
> 
> This kind of trickery may be fragile...
>  
> # Find the right python implementation, check by sending it on over to dave
> for pyimpls in python3 python2 python /usr/bin/python /usr/bin/env python ; do
> 
> And there  you have, you are trying to check for '/usr/bin/env python', but the shell code you wrote will not work the way you are expecting.
> Also, unless you are running on a funny environment that does not have /usr/bin/ in $PATH, the trial for 'python' should be enough, and the /usr/bin/python /usr/bin/env python look redundant. Am I missing something?
>  
>    command -v > /dev/null $pyimpls && exec $pyimpls $0 "$@“
> 
> And the last quote the line above is likely wrong, it is an unicode character.
>  
> done
> # Error code in case things go awry 
> Echo “PYTHON NOT FOUND” >2
> 
> "Echo" ? Are you really running this on Ubuntu? 
> Or you just hacked in on macOS and assumed that it will work everywhere? 
> 
> BTW, Are you aware of the behavior of `command -v` with shell aliases?
> 
> $ alias python=python3
> $ command -v python
> alias python='python3'
> 
> 
> -- 
> Lisandro Dalcin
> ============
> Research Scientist
> Extreme Computing Research Center (ECRC)
> King Abdullah University of Science and Technology (KAUST)
> http://ecrc.kaust.edu.sa/ <http://ecrc.kaust.edu.sa/>

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