Setting selected features in list without specifying their layer using PyQGIS

Question

To get selected features I usually do: layer.selectedFeatures().

Is there a method to retrieve selected features in a list without specifying the layer they belong to ?

I selected features with the "Selection by location" tool:

processing.run("native:selectbylocation", 
                   {'INPUT': "C://path/file1.shp",
                    'PREDICATE':[0,4,7],
                    'INTERSECT':"C://path/file2.shp",
                    'METHOD':0})

The features I am seeking are indeed selected in my QGIS environment. Now I would like to delete them with PyQGIS but I don't know how to retrieve and put them in a list since I didn't create a QgsVectorLayer object for my shapefile.

Do you know a way to either retrieve the selected features or the layer they belong to ?

What is the output of the algorithm? Perhaps that will give you a clue — Matt, Apr 06 '22 at 15:05
The output is a dict object with one key : {"OUTPUT": "C://path/file1.shp"}. So I tried to store that output in a QgsVectorLayer object, but there is 0 selected feature when I try to count them with selectedFeatureCount(). Even though the same layer already displayed in QGIS has some selected features in its attribute table. — Anthony, Apr 07 '22 at 08:21

score 5 · Answer 1 · edited Apr 11 '22 at 11:28

There are most likely several approaches to tackle your issue, but I would probably lean on @Matt's suggestion.

There is a special method for deleting selected features called deleteSelectedFeatures().

Keep in mind that the output of processing will inherit the name of your 'INPUT' variable.

layer1 = QgsProject.instance().mapLayersByName('grid_test2')[0]
layer2 = QgsProject.instance().mapLayersByName('grid_test')[0]
selection = processing.run("native:selectbylocation", 
                   {'INPUT': layer1,
                    'PREDICATE': [0,4,7],
                    'INTERSECT': layer2,
                    'METHOD':0})['OUTPUT']
layer_to_edit = QgsProject.instance().mapLayersByName(selection.name())[0]
layer_to_edit.startEditing()
layer_to_edit.deleteSelectedFeatures()
layer_to_edit.commitChanges()

If you though want to retrieve a list with selected features, then try this:

layer1 = QgsProject.instance().mapLayersByName('grid_test2')[0]
layer2 = QgsProject.instance().mapLayersByName('grid_test')[0]
selection = processing.run("native:selectbylocation", 
                   {'INPUT': layer1,
                    'PREDICATE': [0,4,7],
                    'INTERSECT': layer2,
                    'METHOD':0})['OUTPUT']
layer_to_edit = QgsProject.instance().mapLayersByName(selection.name())[0]
selected_ids = [feat.id() for feat in selection.selectedFeatures()]
layer_to_edit.startEditing()
for fid in selected_ids:
    layer_to_edit.deleteFeature(fid)
layer_to_edit.commitChanges()

References:

Setting selected features in list without specifying their layer using PyQGIS

1 Answers1