Accumulate selections by expression using a for loop (Pyqgis)

Question

I need to run a for loop to select features by their attributes, because the values are within lists (strkey and strvalue). I'm using the following script:

k=0
v=0
layer = iface.activeLayer()
for item in keys:
 listk = strkey[k]
 listv = strvalue[v]
 layer.selectByExpression('\"LINE_ID\" IN ('+listk+') AND \"Declividad\" IN ('+listv+')', QgsVectorLayer.SetSelection)
 v=v+1
 k=k+1

The problem is that only the last feature is selected. Is like every loop the Qgis erases the old selection to select the new feature. Is there a way to accumulate the selections ?

Answer 1

The reason why your selections are being overwritten on each iteration is because you passed QgsVectorLayer.SetSelection for the SelectBehaviour parameter. This sets a new selection each time, removing any existing selection.

Changing your SelectBehaviour argument to QgsVectorLayer.AddToSelection should do the trick.

• Kajo: simple like that! thanks! Do you have a good source so I could study more about this?