qgis - Error when using r.series in a python script

I’m writing a tool script in python and at a certain point I want to use the GRASS tool r.series. I want the algorithem to read all raster files from a folder and calculate the maximum with r.series. The thing is I’m getting the error: “Wrong parameter value: None” when using the code below:

##RasterMaxFinder=name
##Select_directory=Folder
##Save_results=Folder


import glob, os, processing

list = ( Select_directory + "/" + "*.tif" )

processing.runalg('grass7:r.series', list ,False,6,'-10000000000,10000000000',None,30.0, Save_results + "/" + "Output.tif")

It must have something to do with the extend, but I can't figure out what. When I'm using the tool directly in QGIS, erverything works fine. Any Ideas?

Answer

Yes, the extent probably has to be explicitly defined before you can run the algorithm. Seen a few posts about this. The following might work (note that I used grass:r.series and not grass7:r.series):

##RasterMaxFinder=name

##Select_directory=Folder
##Save_results=Folder

import glob, os, processing
from PyQt4.QtCore import QFileInfo
from qgis.core import QgsRasterLayer, QgsRectangle

os.chdir(Select_directory)
list = []
extent = QgsRectangle()

extent.setMinimal()
for raster in glob.glob("*.tif"):
    fileInfo = QFileInfo(raster)
    baseName = fileInfo.baseName()
    rlayer = QgsRasterLayer(raster, baseName)
    # Combine raster layers to list
    list.append(rlayer)
    # Combine raster extents
    extent.combineExtentWith(rlayer.extent())


# Get extent    
xmin = extent.xMinimum()
xmax = extent.xMaximum()
ymin = extent.yMinimum()
ymax = extent.yMaximum()
# Run algorithm
processing.runalg('grass:r.series', list ,False,6,'-10000000000,10000000000',"%f,%f,%f,%f"% (xmin, xmax, ymin, ymax),30.0, Save_results + "/" + "Output.tif")