Iterating over memory layer to run processing algorithm using Python in QGIS?

Question

I am trying to write a python script that iterates over the features of a layer, selects a features and feeds into processing.runalg(). I am pretty sure the selection is going on. However, the processing.runalg("qgis:xxx") bit ocurrs oblivious to the selection! I know there are plenty of similar questions and answers, but I have tried their suggestions and haven't been successful. I though maybe if someone sees the code maybe could help me resolve this.

Here is the code (indents in the for loops might be messed up from formatting):

inter_shpmemory = iface.addVectorLayer(main_directory + "\\" + 
intersect_shpname,"Zone layer",labtype)
specieslayer_mem = iface.addVectorLayer(main_directory + "\\" + 
bd_shpname,"GBIF layer",labtype)

###Create a folder to safe all stuff
newfolder = main_directory + "\\" + "Zonal_GBIF"

if not os.path.exists(newfolder):
    os.makedirs(newfolder)


it = specieslayer_mem.getFeatures( QgsFeatureRequest() )
inputLayerIds = [i.id() for i in it]
#selects all of the input feature and one feature from the clip layer
specieslayer_mem.setSelectedFeatures( inputLayerIds )###is this even 
#needed?



features = inter_shpmemory.getFeatures()

for feature in features:
            indbd_name = feature['simp_name']
            inter_shpmemory.setSelectedFeatures([feature.id()])
            print "Feature ID %d: " % feature.id()
            print indbd_name
            processing.runalg('qgis:clip', specieslayer_mem, inter_shpmemory, newfolder + '\\' + indbd_name +'.shp')  
            inter_shpmemory.setSelectedFeatures([])

specieslayer_mem.setSelectedFeatures([])

I can't get to do it what I want.

Answer 1

The problem can be that, you have to save the selection first. I guess the 'qgis:clip' does not care with the selection. Add this line too, and reload the saved layer with an other line:

QgsVectorFileWriter.writeAsVectorFormat( layer, path + 'admpoly/' + name + ".shp", "system", crs, "ESRI Shapefile", 1)

Answer 2

Instead of making lists, if you want to select all features in a layer, you could use:

layer.selectAll()

Conversely, if you want to remove all selections, you could use:

layer.removeSelection()

---

So in order to get your code to work, you could try using:

inter_shpmemory = iface.addVectorLayer(main_directory + "/" + 
intersect_shpname,"Zone layer",labtype)
specieslayer_mem = iface.addVectorLayer(main_directory + "/" + 
bd_shpname,"GBIF layer",labtype)

###Create a folder to safe all stuff
newfolder = main_directory + "/" + "Zonal_GBIF"

if not os.path.exists(newfolder):
    os.makedirs(newfolder)

specieslayer_mem.selectAll()

features = inter_shpmemory.getFeatures()
for feature in features:
    indbd_name = feature['simp_name']
    inter_shpmemory.setSelectedFeatures([feature.id()])
    print "Feature ID %d: " % feature.id()
    print indbd_name
    processing.runalg('qgis:clip', specieslayer_mem, inter_shpmemory, newfolder + '/' + indbd_name +'.shp')  
    inter_shpmemory.removeSelection()

specieslayer_mem.removeSelection()

---

Note that the "Use only selected features" option must be enabled in:

Processing > Options > General > Use only selected features