Python script problem with Qvariant

Question

I have a problem with a pygis script.

This is a script to load in a shapefile layer from a WFS source and to add 4 extra fields to the attributes: Label, Legende1, Legende2 and PercId. In one of the fields (PercId) a small calculation needs to be done, to reformat an initial string value.

To add the 4 extra fields mentioned, the script apparantly uses Qvariant. Nevertheless, when I run the script the error message is that "Qvariant is not defined". Apparantly, you can add a small line of code at the start (from PyQt4.QtCore import *) to make it work with Qvariant but the script doesn't work. It wont even start in a QGIS 3.x standalone version.

Does anyone have a fix or alternative to add the 4 extra fields to the newly loaded en clipped layer? Because that is where the problem seems to be situated.

The script:

from qgis.core import *
from qgis.gui import *
from PyQt4.QtCore import *

# Define paths and URLs
rootAlgemeen = '//orbit/Orbit server/data/gemeente/44048/Achtergronden/'

# Load existing layers
boundingbox = QgsVectorLayer(rootAlgemeen + 'BoundingBox/Boundingbox44048.shp', 'boundingbox', 'ogr')
gemeentegrens = QgsVectorLayer(rootAlgemeen + 'Grenzen/Gemeentegrens/Apn_gemeentegrens.shp', 'gemeentegrens', 'ogr')
QgsProject.instance().addMapLayers([boundingbox, gemeentegrens])

# Define WFS URLs
WFSrootBB = '&SRSNAME=EPSG:31370&cql_filter=Intersects(SHAPE,POLYGON((91657.679 180064.905, 91657.679 186710.326, 101502.614 186710.326, 101502.614 180064.905, 91657.679 180064.905)))'
WFSrootGRB = 'https://geo.api.vlaanderen.be/GRB/wfs?request=GetFeature&service=wfs&version=2.0.2&typename='

# Load WFS layer
AdpWFS = QgsVectorLayer(WFSrootGRB + 'GRB:ADP' + WFSrootBB, 'WFS GRB Adp', 'wfs')
if not AdpWFS.isValid():
    print("Failed to load WFS layer.")
else:
    QgsProject.instance().addMapLayers([AdpWFS])

    # Start editing the layer
    AdpWFS.startEditing()

    # Define the field names
    percid_field_name = 'PercId'
    canu_field_name = 'CANU'
    
    # Add new fields if they do not already exist
    provider = AdpWFS.dataProvider()
    fields_to_add = [
        QgsField('Label', QVariant.String),
        QgsField('Legende1', QVariant.Int),
        QgsField('Legende2', QVariant.Int),
        QgsField(percid_field_name, QVariant.String)
    ]
    
    provider.addAttributes(fields_to_add)
    AdpWFS.updateFields()

    # Get indices for the new fields
    label_idx = AdpWFS.fields().indexOf('Label')
    legende1_idx = AdpWFS.fields().indexOf('Legende1')
    legende2_idx = AdpWFS.fields().indexOf('Legende2')
    percid_idx = AdpWFS.fields().indexOf(percid_field_name)
    
    # Get the field index for CANU
    canu_idx = AdpWFS.fields().indexOf(canu_field_name)
    
    if canu_idx == -1:
        print(f"Field {canu_field_name} not found.")
    else:
        # Apply the transformation and populate new fields
        for feature in AdpWFS.getFeatures():
            original_value = feature[canu_field_name]
            formatted_value = (
                original_value[:5] + '_' + original_value[5:6] + '_' +
                original_value[6:10] + '_' + original_value[10:12] + '_' +
                original_value[12:15] + '_' + original_value[15:17]
            )
            
            # Set attributes
            feature.setAttribute(percid_idx, formatted_value)
            feature.setAttribute(label_idx, feature[canu_idx])  # Copy value from CANU
            feature.setAttribute(legende1_idx, 0)  # Set Legende1 to 0
            feature.setAttribute(legende2_idx, 0)  # Set Legende2 to 0
            
            # Update feature with new attributes
            AdpWFS.updateFeature(feature)
        
        # Commit changes
        AdpWFS.commitChanges()
    
    # Define the path for saving the shapefile
    rootAdp = '//orbit/Orbit server/data/gemeente/44048/Achtergronden/GRB/GRB_MeestRecent/44048R250/'
    output_path = rootAdp + 'Adp44048B250.shp'
    
    # Save the layer as a shapefile
    error = QgsVectorFileWriter.writeAsVectorFormat(AdpWFS, output_path, 'utf-8', AdpWFS.crs(), 'ESRI Shapefile', onlySelected=False)
    
    if error == QgsVectorFileWriter.NoError:
        print(f'Shapefile saved successfully to {output_path}')
        # Load the saved shapefile into QGIS
        saved_layer = QgsVectorLayer(output_path, 'Adp44048B250', 'ogr')
        if saved_layer.isValid():
            QgsProject.instance().addMapLayer(saved_layer)
            print('Shapefile loaded successfully into QGIS.')
        else:
            print('Failed to load the saved shapefile.')
    else:
        print(f'Error saving shapefile: {error}')

    # Reload original layers
    boundingbox = QgsVectorLayer(rootAlgemeen + 'BoundingBox/Boundingbox44048.shp', 'boundingbox', 'ogr')
    gemeentegrens = QgsVectorLayer(rootAlgemeen + 'Grenzen/Gemeentegrens/Apn_gemeentegrens.shp', 'gemeentegrens', 'ogr')
    QgsProject.instance().addMapLayers([boundingbox, gemeentegrens])

# The script does not exit QGIS, so the layers remain open.