[GRASS-dev] Python Scripting

[stefano negri]

Isn't there a SWIG? I think there is a 'swig' folder in the grass
installation and I remember reading about it on the web.
Stefano.

2008/7/18 Glynn Clements <glynn at gclements.plus.com>:
>
> Dan D'Alimonte wrote:
>
>> 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).
>
> Raster processing in Python is likely to be too slow to be practical.
>
>> 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"] )
>
> This idea has occurred to me. Some comments:
>
> Pass argument values as Python values, e.g. passing multiple values as
> lists, passing numeric types directly, etc, and have the interface
> convert them to strings. Pass the flags as a single string.
>
> module.execute( "r.stats",
>                options = { "input": ["elevation.dem", "slope", "aspect"],
>                            "fs": ",",
>                            "output": "elev.csv" },
>                flags = "q1ng" )
>
> Provide a lower-level function which simply generates the command to
> pass to Popen(), for cases where you want to interact with the child
> process.
>
> Provide an intermediate function which starts the process, returning
> an object from which you can obtain structured progress information:
> percentage complete, any messages along with their type (debug, info,
> warning), etc.
>
> --
> Glynn Clements <glynn at gclements.plus.com>
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