eligibleLayer = QgsVectorLayer("/home/usr/Desktop/eligible_areas.shp", "eligible_areas", "ogr")

if not eligibleLayer.isValid():
    print "Eligible areas layer failed to load!"

lProvider = eligibleLayer.dataProvider()
lProvider.addAttributes( [ QgsField("Area",QVariant.Double) ] )

area = 0
for gFeat in eligibleLayer.getFeatures():
    calculator = QgsDistanceArea()
    calculator.setEllipsoid('WGS84')
    calculator.setEllipsoidalMode(True)
    geom = gFeat.geometry()
    landArea = gFeat.attributes()[gProvider.fieldNameIndex('Area')].toDouble()[0]
    if geom.isMultipart() is False: # if only simple polygon, calculate only for this
        polyg = geom.asPolygon() #transform to list of points
        if len(polyg) > 0:
            area = calculator.measurePolygon(polyg[0])

    else: #is Multipart
        multi = geom.asMultiPolygon()
        for polyg in multi:
            area = area + calculator.measurePolygon(polyg[0])