pyqgis - QGIS test rules with python

In QGIS 2.14 one can check if a rule gives results:

Is it possible to do this programmatically with python console? I would look for a way to iterate over all layers and there rules (nested rules!) and print those (layer_name:rule_name) which do not have results.

Answer

Perhaps this answer can fully solve your question.

Run this code snippet in the QGIS Python Console:

for layer in QgsMapLayerRegistry.instance().mapLayers().values(): # Iterate layers
    if type(layer) == QgsVectorLayer and layer.hasGeometryType():
        r = layer.rendererV2()
        if r.type() == 'RuleRenderer':
            for rule in r.rootRule().children(): # Iterate rules

                if rule.filter(): # Filter out empty rules
                    request = QgsFeatureRequest( rule.filter() )
                    count = len( [f for f in layer.getFeatures( request )] )
                    print layer.name() + ' : ' + rule.label() + ' : ' + rule.filterExpression() + ' : ' + str(count)

The first for loop iterates layers, the second one iterates layer rules. First if clause ensures we use vector layers, the second one ensures we only use vector layers with a rule based style, and the last one filters out empty rules.

The result is a list with layer names, rule labels, rule expressions, and the corresponding count, like this:

my_point_layer : My Rule :  "my_code" = '1': 6
my_point_layer : My 2nd Rule :  "my_code" IS NULL : 0
my_polygon_layer : My Polygon Rule :  "area" > 100 : 2

my_polygon_layer : My 2nd Polygon Rule :  "area <= 100 : 28

You could then use the count variable to filter only those with 0 features, which was your original purpose.

Hope this solves your question.