Checking whether vector layer is empty or not with PyQGIS

Question

I am working on intersections of a number of buffers with one another. When two particular buffers have no intersection, applying intersection function on them produces an empty layer which I want to delete. But how do I check if the intersection result produced is an empty layer or not? Is there any inbuilt function which I can use in my code?

• Germán Carrillo: @Mr.Che, better this one: qgis.org/pyqgis/3.6/core/…
• Comrade Che: qgis.core.QgsVectorLayer.hasFeatures() method qgis.org/pyqgis/master/core/…

Answer 1

There are several approaches available to identify whether a vector layer is empty:

Solution 1: .hasFeatures() method of the QgsVectorLayer class

Determines if this vector layer has features.

Since QGIS 3.4

from qgis.core import QgsProject, Qgis
layer = QgsProject.instance().mapLayersByName("BW — Empty")[0]
if layer.hasFeatures() == 0:
# or if layer.hasFeatures() == Qgis.FeatureAvailability.NoFeaturesAvailable:
 print(f"The layer '{layer.name()}' is empty.")

See also the return Qgis.FeatureAvailability.NoFeaturesAvailable (since QGIS 3.36) of the .hasFeatures() method.

Solution 2: .featureCount() method of the QgsVectorLayer class

Returns feature count including changes which have not yet been committed If you need only the count of committed features call this method on this layer's provider.

from qgis.core import QgsProject
layer = QgsProject.instance().mapLayersByName("BW — Empty")[0]
if layer.featureCount() < 1:
 print(f"The layer '{layer.name()}' is empty.")

It implements the QgsFeatureSource class.

Solution 3: .empty() method of the QgsVectorDataProvider class

Returns True if the layer does not contain any feature

Since QGIS 3.4

from qgis.core import QgsProject
layer = QgsProject.instance().mapLayersByName("BW — Empty")[0]
provider = layer.dataProvider()
if provider.empty():
 print(f"The layer '{layer.name()}' is empty.")