How to set the color of a feature depending on field attributes with PyQGIS?

Question

from PyQt4.QtCore import *
from PyQt4.QtGui import *
def Symbology():
    canvas = qgis.utils.iface.mapCanvas()
    layer = qgis.utils.iface.activeLayer()
    for feat in layer.getFeatures():
        Value = feat['field']
        print Value 
        if Value != '':
            featColor = {
                  Value :  ('red',Value ),
                    }
        elif Value == '':
             featColor = {
                  '' :  ('green','')
                    }
        ranges = []
        for rType, (color, label) in featColor.items():
            print rType,(color, label)
            symbol = QgsSymbolV2.defaultSymbol(layer.geometryType())
            symbol.setColor(QColor(color))
            category = QgsRendererCategoryV2(rType, symbol, label)
            ranges.append(category)

    # create the renderer and assign it to a layer
    expression = 'field' # field name
    renderer = QgsCategorizedSymbolRendererV2(expression, categories)
    layer.setRendererV2(renderer)
    canvas.zoomToSelected()
    layer.removeSelection()

Here i have to set based on the feature value but when i am executing this script it is setting for only one value. I f i want to set colors based on the values how can i do that?

The value contains for example Value = ['x','y',NULL]

Answer 1

Did you consider rule based rendering instead of categorized rendering?

https://qgis.org/api/2.18/classQgsRuleBasedRendererV2.html

rsp.

https://qgis.org/api/classQgsRuleBasedRenderer.html for QGIS 3