qgis - Using v.distance python script parameter with PyQGIS?

This question is an extension of Copying code generated when you put data into GUI via QGIS Plugins?

I have a Python file I want to run on two loaded layers in QGIS. The layers are TestPhotos (point) and TestObj (point). The tool I want the Python file to run is v.distance.

The column in TestObjects I use in v.distance is OBJ_ID

The Python file is called Test1.py. I have this code:

import processing

processing.runalg('grass7:v.distance', 'TestPhotos','point,line,area','TestObj','point,line,area',-1.0,-1.0,'to_attr','OBJ_ID','OBJ_ID',None,-1.0,0.0001,'nearestobj','distance')

I get the following output using the QGIS Python console:

execfile(u'C:/OSGeo4W64/Test1.py'.encode('mbcs'))
Error: Wrong parameter value: None

I believe it is associated with the v.distance GRASS_REGION_PARAMETER parameter. Any idea how to deal with this to get the Python script working?

EDIT1 - responding to comment

When I typed in processing.alghelp('grass7:v.distance'), i got this:

>>>import processing
>>>processing.alghelp('grass7:v.distance') 

    ALGORITHM: v.distance - Finds the nearest element in vector map 'to' for elements in vector map 'from'.
        from 
        from_type 

        to 
        to_type 
        dmax 
        dmin 
        upload 
        column 
        to_column 
        GRASS_REGION_PARAMETER 
        GRASS_SNAP_TOLERANCE_PARAMETER 
        GRASS_MIN_AREA_PARAMETER 

        from_output 
        output 

EDIT2

When I try 'Test.py' with the following code:

import processing 
TestPhotos = QgsVectorLayer('c:\OSGeo4w64\TestFiles\TestPhotos.shp', 'TestPhotos', 'ogr')
TestObj = QgsVectorLayer('c:\OSGeo4w64\TestFiles\TestObj.shp', 'TestObj', 'ogr')

extent = TestPhotos.extent()

xmin = extent.xMinimum()
xmax = extent.xMaximum()
ymin = extent.yMinimum()
ymax = extent.yMaximum()

processing.runalg(\
'grass7:v.distance', \
TestPhotos,\
'point,line,area',\
TestObj,\

'point,line,area',\
-1.0,-1.0,\
'to_attr',\
'OBJ_ID',\
'OBJ_ID',\
"%f,%f,%f,%f" %(xmin, xmax, ymin, ymax),\
-1.0,0.0001,\
'C:\OSGeo4W64\TestFiles\Outputfile0.shp',\
'C:\OSGeo4W64\TestFiles\Outputfile1.shp')  

The output files are correctly generated with the above code. But they are not loaded in QGIS.

Answer

You get the error because an extent is required and it can't be set to None.

Before posting the code, I think there is another error linked to the input layers: they should be added as objects, and not as strings. If 'TestPhotos' and 'TestObj' are the names with which they are loaded in the Layers Panel, you may call them in this way (the following is a general method because I don't know if you are using the Python Console or a new script from the Processing Toolbox):

TestPhotos = QgsVectorLayer('path to the vector layer', 'TestPhotos', 'ogr')
TestObj = QgsVectorLayer('path to the vector layer', 'TestObj', 'ogr')

Then, since it seems you want to use the minimum covering extent, you may try to use the following code:

import processing


extent = TestPhotos.extent()
xmin = extent.xMinimum()
xmax = extent.xMaximum()
ymin = extent.yMinimum()
ymax = extent.yMaximum()

processing.runalg('grass7:v.distance', TestPhotos,'point,line,area',TestObj,'point,line,area',-1.0,-1.0,'to_attr','OBJ_ID','OBJ_ID',"%f,%f,%f,%f" %(xmin, xmax, ymin, ymax),-1.0,0.0001,'nearestobj','distance')

instead of what you have provided.

EDIT Perhaps, also the 'distance' parameter could be wrong because it should be a path or None.