[GRASS-dev] r.mapcalc in Python script (parse error)

[Margherita Di Leo]

Hi,

On Wed, Oct 26, 2011 at 9:30 PM, Glynn Clements <glynn at gclements.plus.com>wrote:

>
> Margherita Di Leo wrote:
>
> > I need a little help with r.mapcalc syntax in Python script. I want to
> > convert the following formula:
> >
> > grass.run_command('r.mapcalculator', amap = r_stream+'_nothin' , formula
> =
> > '%s*%s' % (r_stream+'_nothin', r_mask) , outfile = r_stream+'_nothin',
> > overwrite = True)
> >
> > I want to use r.mapcalc instead of r.mapcalculator. So I write:
> >
> > grass.mapcalc("$r_stream_nothin = $r_stream_nothin * $r_mask",
> >                       r_mask = r_mask,
> >                       r_stream_nothin = r_stream+'_nothin')
> >
> > but I get parse error. What's the correct way to do this? The aim is to
> add
> > the suffix '_nothin' to the existing variable name r_stream.
>
> There's nothing obviously wrong with the above code, although you
> should probably quote the map names, i.e.:
>
>        grass.mapcalc("'$r_stream_nothin' = '$r_stream_nothin' * '$r_mask'",
>          ...
>

This doesn't work, I keep getting Parse error. I can find a workaround for
my script, but I was just curious whether I did it wrong or grass doesn't
allow this kind of parsing. Glynn, thanks for precious hints.


>
> Map names which contain symbols need to be quoted, otherwise e.g. a
> map named "map-name" will be parsed as a subtraction.
>
> Check the values of r_stream and r_mask with e.g.:
>
>        print repr(r_stream), repr(r_mask)
>
> Running 'g.gisenv set=DEBUG=1' prior to the script will enable some
> debugging information, including the exact r.mapcalc command.
>
> Also, using the same map as both input and output is unwise. It
> appears to work, at least for simple cases, but shouldn't be relied
> upon.
>
> --
> Glynn Clements <glynn at gclements.plus.com>
>

regards,
madi



-- 
Eng. Margherita Di Leo
Ph.D. Candidate
Methods and Technologies for Environmental Monitoring
Department of Environmental Engineering and Physics (DIFA)

University of Basilicata
Campus Macchia Romana
85100 - Potenza
Italy

Office: +39-0971205360
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