How to select specific fields using getFeatures() without getting all of them in QGIS-3.10

Question

So I'm trying to convert code from ArcGIS to QGIS. The part I am at right now is converting:

lst_fields = ["full_id", "osm_id", "osm_type", "boundary", "is_in", "leisure", "name", "type", "landuse"]
with arcpy.da.UpdateCursor(urh, lst_fields) as cursor:
    for row in cursor:
         ...

However, with QGIS I have to instead use:

with edit(vector_layer):
    for row in vector_layer.getFeatures(request):

I did not find a way to get only the fields specified in the list apart from doing another for loop and doing this and then storing the values in another list:

row.attributes()[row.fields().indexFromName('boundary')]

The code I have right now is:

lst_fields = ["full_id", "osm_id", "osm_type", "boundary", "is_in", "leisure", "name", "type", "landuse"]
vector_layer = QgsVectorLayer(repertoire+'\\protected_areas.shp','ogr')
request = QgsFeatureRequest().setSubsetOfAttributes(lst_fields, vector_layer.fields())

with edit(vector_layer):
    for row in vector_layer.getFeatures(request):
        print(lst_fields)
        print(row.fields().names())

The first print gives this:

['full_id', 'osm_id', 'osm_type', 'boundary', 'is_in', 'leisure', 'name', 'type', 'landuse']

The second print gives this:

['full_id', 'osm_id', 'osm_type', 'boundary', 'is_in', 'leisure', 'name', 'type', 'wikidata', 'wikipedia', 'landuse', 'name_de', 'sagns_id', 'website']

I thought the request would make it so the two prints would give the same result. I will say what my question is again just in case it wasn't clear:

Is there a way to only get the fields specified in the list like it was possible in arcGIS without the need of another for loop that would save the value of 1 field at a time.

Answer 1

German pointed out already that QgsFeatureRequest.setSubsetOfAttributes([li_required_idx]) returns None for any attribute not in li_required_idx. With some list comprehension it is possible to get li_attr equal to li_fields in the following code:

lyr = iface.activeLayer()
li_required_fields = ["POP_EST", "NAME_RU", "POP_DENSITY"]
request = QgsFeatureRequest().setSubsetOfAttributes(li_required_fields, lyr.fields())

for f in lyr.getFeatures(request):
    li_attr = [attr for attr in f.attributes() if attr is not None]
    print(li_attr)

Now all request attributes (li_required_fields) are in (li_attr). If you want to get 1 attribute at a time, then using the f[required_attr] is probably the best approach as German suggested.