Updating attribute table using PyQGIS?

Question

I'm tring to update the attributes of a field based on the attributes of another field as follows:

def vulProcessing(layer):
    layerV=QgsVectorLayer(layer,'','ogr')
    layerV.startEditing()
    for feature in layerV.getFeatures():
        if feature['Old'] == "H":
            feature['New'] = 'ddw'
    layerV.updateFeature(feature)
    layerV.commitChanges()

The code runs without error but the attribute table does not update.