[GRASS-dev] Python Scripting

[Glynn Clements]

Michael Barton wrote:

> > 	subprocess.call([
> > 		"v.extract",
> > 		"input=%s" % os.getenv("GIS_OPT_INPUT"),
> > 		"output=%s_%s" % (os.getenv("GIS_OPT_OUTPUT"), i),
> > 		"type=point", "layer=1", "new=-1", "list=%s" % i])
> 
> Glynn,
> 
> How do subprocess.call and subprocess.Popen compare for running GRASS  
> commands from inside Python scripts? Is call easier than Popen in this  
> context?

subprocess.call is a convenience function for the simplest case where
you don't need to interact with the child process beyond waiting for
it to finish; it's defined as:

	def call(*args, **kwargs):
	    """Run command with arguments.  Wait for command to complete, then
	    return the returncode attribute.
	
	    The arguments are the same as for the Popen constructor.  Example:
	
	    retcode = call(["ls", "-l"])
	    """
	    return Popen(*args, **kwargs).wait()

It behaves like system(), but without the shell (so you don't have to
deal with /bin/sh syntax vs cmd.exe syntax, spaces and other shell
metacharacters in argument values, etc).

It's roughly equivalent to os.spawnvp(P_WAIT,...), which is deprecated
in favour of the subprocess module. Most of the other os.* functions
are similarly deprecated, except for the os.exec* family (for which
the main use is executing g.parser).

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