[GRASS-user] Running an external executable file from a Python Script

GRASS GRASS user
1

Greetings all,

I have a python script from where I need to run an external binary (in Windows). This external binary (not developed by me) uses an input_parameter file to configure binary and get other parameters. The problem is that this binary requires that in my active folder I have my parameter file. Example: If I want to run this binary (outside GRASS Python Scripts) i open cmd, go to a folder where I have a parameter file (e.g. c:\delete (cd c:\delete)) Then I can run this binary as long as I have my parameter file in my "active folder" like this (c:\tool\training.exe). What I mean is that in my active folder I do not need to have my binary only my parameter file.
My question is, when I'm running a GRASS python Script what is my active folder in order to place there my Parameter file? Or, is there any way to change my "active folder" while I'm running GRASS python Script?

Hope I was clear enough in this email since this was unexpected for me.

Thanks
Antonio

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2

António Rocha wrote:

My question is, when I'm running a GRASS python Script what is my active
folder in order to place there my Parameter file? Or, is there any way
to change my "active folder" while I'm running GRASS python Script?

By "active folder", I presume that you're referring to the current
directory (aka working directory, current working directory or CWD).
This is inherited from the calling process; e.g. if you run a script
from a shell, the script's current directory will be the shell's
current directory.

When executing a command via subprocess.Popen(), you can specify its
current directory via the cwd= parameter. The grass.Popen() and
grass.call() functions accept this parameter, as do all of the
grass.*_command() functions for running GRASS modules.

You can change the current directory for the current process using
os.chdir(), but that should normally be avoided, as any relative
filenames will then be interpreted relative to the new current
directory, whereas the user probably intended them to be relative to
the initial current directory.

--
Glynn Clements <glynn@gclements.plus.com>

3

Hi (Olá)

in order to figure out what is your current working folder (or active
folder) you can do

# python code

import os
os.getcwd()

# end of code

This will return a string with your current working folder.
As Glyn is stating, if you are going to call this external binary from
within a python script you can use a grass.Popen object (or just a
normal subprocess.Popen).
The grass.Popen object allows you to capture your external binary's
output and (eventual) error messages.

In the following example, I'm running the 'ls -l' external command,
using the /home/Documents directory as a working directory for the
external command. Please adapt to your problem / operating system:

# python code

import grass.script as grass

externalCommand = ["ls", "-l"] # note that it is a list
externalProcess = grass.Popen(externalCommand, stdout=grass.PIPE,
stderr=grass.PIPE, cwd="/home/ricardo/Documents")
sdtout, stderr = externalProcess.communicate()

# to show the output of your external program
print(stdout)

# end of code

Hope it helps :wink:

2011/3/10 Glynn Clements <glynn@gclements.plus.com>:

António Rocha wrote:

My question is, when I'm running a GRASS python Script what is my active
folder in order to place there my Parameter file? Or, is there any way
to change my "active folder" while I'm running GRASS python Script?

By "active folder", I presume that you're referring to the current
directory (aka working directory, current working directory or CWD).
This is inherited from the calling process; e.g. if you run a script
from a shell, the script's current directory will be the shell's
current directory.

When executing a command via subprocess.Popen(), you can specify its
current directory via the cwd= parameter. The grass.Popen() and
grass.call() functions accept this parameter, as do all of the
grass.*_command() functions for running GRASS modules.

You can change the current directory for the current process using
os.chdir(), but that should normally be avoided, as any relative
filenames will then be interpreted relative to the new current
directory, whereas the user probably intended them to be relative to
the initial current directory.

--
Glynn Clements <glynn@gclements.plus.com>
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--
___________________________ ___ __
Ricardo Garcia Silva