How to select multi-part polygons from a layer using PyQGIS

My script is -

# Find all multipart features in the active layer
l = iface.activeLayer()

iter = l.getFeatures()
geoms = []
for feature in iter:
    geom = feature.geometry()
    if geom.isMultipart():
        l.select(feature.id())
        geoms.append(geom)

print 'There are %i multipart features in this layer' % len(geoms)

I don't know the exact problem with this script. Using this script in the Python console should select all multi part features in the active layer but in my case no multi section polygons fetched, while I can easily see multi section polygons exists in my polygon file.

Answer

This is an easier alternative.

layer = iface.activeLayer()   
expr = QgsExpression( "num_geometries( $geometry ) > 1" )
it = layer.getFeatures( QgsFeatureRequest( expr ) )    
ids = [i.id() for i in it]  

Now you can know how many features are multi-part:

print 'There are {} multipart features in this layer'.format(len(ids))

And even select multi-part features:

layer.setSelectedFeatures( ids )