[GRASS-user] GRASS-Python Script: Check if output already exists, overwrite

[Johannes Radinger]

Thank you! The grass.script.overwrite() function was the one I was looking
for. :)


On Thu, Apr 11, 2013 at 1:00 PM, Glynn Clements <glynn at gclements.plus.com>wrote:

>
> Johannes Radinger wrote:
>
> > I would like to check if the file defined as output in a python script
> > already exists and fire an error when it exists and the overwrite flag is
> > not set. Furhtermore I'd like
> > to check this already in the beginning before all calculations in the
> > script are executed.
>
> g.parser should do this automatically.
>
> If an option has "new" in the gisprompt field, G_parser() checks that
> either the file/map/etc doesn't exist or overwrite is enabled.
>
> The only time you should need to do this manually is if an output name
> isn't simply an option value (e.g. r.mapcalc's output maps are
> specified in the expression, r.rgb takes an output "template" to which
> it appends a .r/.g/.b suffix, etc).
>
> > I thought about something like:
> >
> > output = options['output']
> >     if (grass.find_file(name = output, element = 'cell')['file'] and
> > grass.read_command("g.gisenv", get = "GRASS_OVERWRITE")!=1):
> >         grass.fatal(_("Output file exists already, either change output
> > name or set overwrite-flag"))
> >
> > but what is the correct way to get the information if the overwrite flag
> is
> > set
> > or not for that script? The GRASS-OVERWRITE variable is not set although
> > the script is launched with --overwrite. So how to get this info?
>
> The grass.script.overwrite() function returns True if overwrite is
> enabled. Also, os.environ['GRASS_OVERWRITE'] will have been set to '1'
> by grass.script.parser() so that the overwrite status propagates down
> to any commands executed by the script.
>
> --
> Glynn Clements <glynn at gclements.plus.com>
>
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