[GRASS-user] RE: grass-user Digest, Vol 61, Issue 42 [SEC=UNCLASSIFIED]

[Andrew MacIntyre]

> Date: Wed, 18 May 2011 14:53:25 +0200
> From: "Johannes Radinger" <JRadinger at gmx.at>
> Subject: Re: [GRASS-user] Re: Using temp files in Grass Script
> To: Glynn Clements <glynn at gclements.plus.com>
> Cc: grass-user at lists.osgeo.org
> Message-ID: <20110518125325.274840 at gmx.net>
> Content-Type: text/plain; charset="utf-8"
> 
> 
> -------- Original-Nachricht --------
> > Datum: Tue, 17 May 2011 13:11:41 +0100
> > Von: Glynn Clements <glynn at gclements.plus.com>
> > An: "Johannes Radinger" <JRadinger at gmx.at>
> > CC: grass-user at lists.osgeo.org
> > Betreff: Re: [GRASS-user] Re: Using temp files in Grass Script
> 
> >
> > Johannes Radinger wrote:
> >
> > > I found that thread about temporary maps...
> > >
> > > e.g in my case in my python script i use:
> > >
> > >     #Convert river from vector to raster format
> > >     grass.run_command("v.to.rast",
> > >                       input = "river_gen",
> > >                       overwrite = True,
> > >                       output = "river_raster",
> > >                       use = "val",
> > >                       value = res)
> > >
> > >     #Thinning the rastarized river
> > >     grass.run_command("r.thin",
> > >                       input = "river_raster",
> > >                       overwrite = True,
> > >                       output = "river_raster_thin")
> > >
> > > and here is the map river_raster only temporary for the thinning
> > > process and the river_raster_thin is used for further calculations.
> > > At the moment I have a g.remove to remove the river raster after
> > > the thinning process but should I handle that with temporary files/maps
> > > and if yes how is that exactly done in my python script?
> >
> > 1. In general, you should make an attempt at ensuring that temporary
> > map names won't conflict with any existing map name. The usual
> > approach is to include both ".tmp" and the PID in the map name, e.g.:
> >
> > 	import os
> > 	...
> > 	global tmpmap
> > 	tmp_map = 'river_raster.tmp.%d' % os.getpid()
> >
> > 2. Deletion should ideally be handled using an exit handler, e.g.:
> >
> > 	import os
> > 	import atexit
> > 	import grass.script as grass
> >
> > 	tmp_map = None
> >
> > 	def cleanup():
> > 	    if tmp_map:
> > 		grass.run_command('g.remove', rast = tmp_map, quiet =
> True)
> >
> > 	def main():
> > 	    global tmpmap
> > 	    tmp_map = 'river_raster.tmp.%d' % os.getpid()
> > 	    ...
> >
> > 	if __name__ == "__main__":
> > 	    options, flags = grass.parser()
> > 	    atexit.register(cleanup)
> > 	    main()
> >
> > Using an exit handler ensures that the temporary map gets removed
> > regardless of how the script terminates (e.g. if it terminates due to
> > an exception).
> 
> Thank you for your nice examples how to do that with tmp files and the exit
> handler.
> 
> Just some questions:
> 1) is the PID also used on windows systems? so can it be integrated in a script
> which also windows users want to use? Is it correct that the PID is the same
> value for running the whole script one time?
> 
> 2) what exactly does the "global tmpmap"?
> 
> 3)I've got a lot of tmp-files which will be created during the process, so is
> there and option to tell the g.remove that all maps containing .tmp.%d' %
> os.getpid() in the end should be removed instead of typing all the tmp map
> files into the list of g.remove.
> 
> 4) so the whole thing works that in the end all the tmp maps are deleted
> after the processing of the script and after an exception etc.

Rather than use a simple global variable as per Glynn's example, use a list:

	tmp_map = []

Any time you create a temporary file name, append it to the list:

	tmp_fn = '...'
	tmp_map.append(tmp_fn)

In your cleanup handler, scan the list:

	def cleanup():
	    while tmp_map:
	        tfn = tmp_map.pop()
	        grass.run_command('g.remove', rast = tfn, quiet = True)

Using a list like this removes the need for the global statements, as you only manipulate the list rather than assign new objects to the global variable.

-------------------------> "These thoughts are mine alone!" <---------
Andrew MacIntyre           Operations Branch
tel:   +61 2 6219 5356     Communications Infrastructure Division
fax:   +61 2 6253 3277     Australian Communications & Media Authority
email: andrew.macintyre at acma.gov.au            http://www.acma.gov.au/



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