[GRASS-dev] grass and python

[Michael Barton]

William,

See additional responses below.

Michal
__________________________________________
Michael Barton, Professor of Anthropology
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton



> From: William Kyngesburye <woklist at kyngchaos.com>
> Reply-To: William Kyngesburye <kyngchaos at kyngchaos.com>
> Date: Sat, 12 Aug 2006 10:15:15 -0500
> To: David Finlayson <david.p.finlayson at gmail.com>
> Cc: <grass-dev at grass.itc.it>
> Subject: Re: [GRASS-dev] grass and python
> 
> But, as long as the Python app sets up and maintains that shell
> environment, shouldn't the shell scripts work, if run from the Python
> environment? something like (pardon, just getting started with python):

Bash scripts will work if it sets up a Bash environment, but not necessarily
if it sets up another shell environment. The command prompt in Unix is
actually a running shell program that provides an interface for shell
commands. There are multiple shells possible, but Bash has become a common
denominator for GRASS and many other programs.

> 
> os.environ to set up environment (probably what your experimental
> python startup does)

It use os.environ to read currently set environmental variables. There is
some cautioning in the Python manual about using it to set environmental
variables on different platforms.

> 
> os.popen to run the shell script - uses os.environ setup, or is that
> where it needs a running shell?  It's possible to start it in a
> shell, like a new Terminal window on OS X, tho a bit messy.  Maybe
> there's a python-driven shell interpreter?

The Python cmd module may do this, but I haven't yet experimented with it.
Maybe David knows. 

> 
>> Many standard GRASS commands are really shell scripts. Every single
>> one of them will need to be ported to your new shell if this isn't
>> compatible with Bash. I stopped working on this when I realized how
>> disruptive this was going to be (and how unlikely this would be
>> supported by the core GRASS community). I don't think the vast
>> majority of GRASS developers want to move to a Python environment
>> (or Ruby or Perl or cmd.exe, etc). So, basically, this is an idea
>> dead-on-arrival. It would amount to a fork of GRASS and new users
>> would have a terrible time figuring out which shell they were
>> supposed to be using for each script.
>> 
>> I think that GRASS is intimately tied to a Posix-compliant shell.
>> There needs to be a standard macro-language for scripting and Bash
>> seems as good as any.
>> 
> Coming from a more object-oriented programming perspective, I find
> unix shell scripting to be a nightmare.
> 
> If the wxpython GUI takes off as the main GRASS GUI, there will
> probably be less resistance to moving to Python for all or most GRASS
> scripting.

We'll see. I've done my share of shell scripting and do like what I'm
learning about Python. I'm especially encouraged that so many other people
know something about it too.

Michael