PyQGIS layer action: Select features within buffer having the same field value

Question

By means of a PyQGIS layer action, I am looking for a way to select all polygon features within a buffer polygon sharing a certain field value (e. g. provinces belonging to the same country) with the feature I have clicked on. I got stuck in the part of the code combining the getFeatures method with a selecting expression, which throws the following TypeError:

Traceback (most recent call last):
 File "", line 26, in 
TypeError: QgsFeatureRequest(): arguments did not match any overloaded call:
 overload 1: too many arguments
 overload 2: argument 1 has unexpected type 'str'
 overload 3: argument 1 has unexpected type 'str'
 overload 4: argument 1 has unexpected type 'str'
 overload 5: argument 1 has unexpected type 'str'
 overload 6: argument 1 has unexpected type 'str'

The full code is:

from qgis.utils import iface
 
layer_id = '[%@layer_id%]'
feature_id = [%$id%]
feature_name = '[%name%]'
field_name = 'iso_a2'
field_value = '[%iso_a2%]'
expression = f'"{field_name}" = \'{field_value}\''
 
layer = QgsProject.instance().mapLayer(layer_id)
buffer_layer = QgsVectorLayer("Polygon?crs=epsg:3857&field=fid:integer", f'{feature_name}_buffer_500km', "memory")
buffer_layer.setCrs(QgsCoordinateReferenceSystem(3857))
buffer_distance = 500000
for feature in layer.getFeatures([feature_id]):
 geom = feature.geometry()
 buffer = geom.buffer(buffer_distance, 5)
f = QgsFeature()
f.setGeometry(buffer)
buffer_layer.dataProvider().addFeatures([f])
QgsProject.instance().addMapLayer(buffer_layer)
iface.setActiveLayer(layer)
layer2 = layer.getFeatures(QgsFeatureRequest(expression)) # This line throws the TypeError
intersecting_features = [
 p.id() 
 for p in layer.getFeatures(buffer.boundingBox())
 if p.geometry().intersects(buffer)
 ]
if intersecting_features:
 layer2.selectByIds(intersecting_features)

Data for this working example comes from the natural earth data set, layer: ne_50m_admin_1_states_provinces (used crs: 3857)

How has the code to be changed in order to get the intended result?

Answer 1

With the help of this answer, I finally found a solution:

from qgis.utils import iface
 
layer_id = '[%@layer_id%]'
feature_id = [%$id%]
feature_name = '[%name%]'
field_name = 'iso_a2'
field_value = '[%iso_a2%]'
expression = f'"{field_name}" = \'{field_value}\''
 
layer = QgsProject.instance().mapLayer(layer_id)
buffer_layer = QgsVectorLayer("Polygon?crs=epsg:3857&field=fid:integer", f'{feature_name}_buffer_500km', "memory")
buffer_layer.setCrs(QgsCoordinateReferenceSystem(3857))
buffer_distance = 500000
for feature in layer.getFeatures([feature_id]):
 geom = feature.geometry()
 buffer = geom.buffer(buffer_distance, 5)
f = QgsFeature()
f.setGeometry(buffer)
buffer_layer.dataProvider().addFeatures([f])
QgsProject.instance().addMapLayer(buffer_layer)
iface.setActiveLayer(layer)
intersecting_countries_ids = [
 c.id()
 for c in layer.getFeatures(buffer.boundingBox())
 if (c.geometry().intersects(buffer)
 )
 ]
if intersecting_countries_ids:
 layer.selectByIds(intersecting_countries_ids)
layer.selectByExpression(expression, QgsVectorLayer.IntersectSelection)