Finding area of individual multipart parts using PyQGIS

Question

Im trying to find the area of each part in multipart polygons. I know some polygons have multiple parts, so why cant I access the individual polygon parts like this (why is parts list empty):

lyr = iface.activeLayer()
f = next(lyr.getSelectedFeatures())
parts = [p for p in f.geometry().parts()]

print(len(f.geometry().asMultiPolygon()))
print(parts)

2
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Answer 1

Try to use f.geometry().constParts() instead.

https://qgis.org/pyqgis/3.16/core/QgsGeometry.html?#qgis.core.QgsGeometry.constParts

Answer 2

After accessing the selected features, you need to loop on every geometry of the each feature first, then loop again on every part of the feature to calculate the individual acreage of each part of a multipart polygon.

Here is the code that worked for me:

lyr = iface.activeLayer()
features = lyr.getSelectedFeatures()
for feature in features:
    geoms = feature.geometry()
    print('Total area = {0} m2'.format(geoms.area()))
    
    for p in geoms.parts():
        print('Sub-area = {0} m2'.format(p.area()))

The output is:

Total area = 112077414.63030124 m2
Sub-area = 40200853.98864746 m2
Sub-area = 35989267.033569336 m2
Sub-area = 35887293.60803223 m2