[GRASS-dev] Python Scripting

[Dan D'Alimonte]

I'm curious if any though has been given to developing an actual GRASS
library for Python that goes beyond calling executables with system calls?

I'm thinking about a model that encapsulates the GRASS environment and
allows for both low-level processing like the C library, and high-level
use of existing modules like shell scripts.

I'll admit I have not given this a lot of though, but a hypothetical,
and  quickly thought-out, example could be something like:



from grass import module, layer, cell, parser

def r_add(inLayers, outLayer):
	for outCell in outLayer.cells:
		sum = cell(type=outLayer.cellType)
		for l in inLayers:
			c = l.getCellAtSameLocation(outCell)
			if c.value==cell.null:
				sum.value = cell.null
				break
			sum.value += c.value
		outCell.value = c.value
	outLayer.commit()
		
if __name__ == "__main__":
	# Set up module information here
	# Set up and run parser
	# Open input layers
	# Create new layer for output
	# call r_add()
	# close layers	



I don't know if this would even be feasible, but I think it would make a 
nice addition to GRASS's Python support. If done right it would even 
allow other python-based GRASS modules to be called-on without having to 
make a system-call (eg. from raster_add import r_add).

As to existing modules, what about a helper function to access then?

module.executeModule( name="r.stats", options={ "input": 
"elevation.dem,slope,aspect", "fs": ",", "output": "elev.csv"}, 
flags=["q", "1", "n", "g"] )

It was just a thought, and would require a lot more thought and work to
design properly. I, frankly, do not have enough understanding of GRASS 
internals to even know where to begin.


-- Dan.