Determining number of vertices of selected object in QGIS 3

Question

How can I determine how many vertices/nodes a selected feature has in QGIS 3?

Answer 1

You can use the following script in QGIS Python Editor. Select a layer, run the script and select a feature.

def n_vertices(selected, _, __):
    n = len(selected)
    
    if n == 1:
        g = iface.activeLayer().selectedFeatures()[0].geometry()
        print(len([v for v in g.vertices()]))
    elif n > 1:
        print("Select only one feature")
        
iface.activeLayer().selectionChanged.connect(n_vertices)

Answer 2

num_points($geometry) returns the number of vertices of the current feature.

Answer 3

Try using the "Identify Features" tool (Ctrl+Shift+I) from the Attributes Toolbar.

Click on the target feature and check the (Derived) tab, where you may see the 'Vertices' attribute