vertexDataAsPoint2D() in QSGGeometry returns only one point

trying to create Scene Graph - Custom Geometry (https://doc.qt.io/qt-5/qtquick-scenegraph-customgeometry-example.html)  in Pyside2, but getting following error :
  File "/BezierCurveProj/main.py", line 119, in updatePaintNode
    vertices[i].set(x, y)
TypeError: 'PySide2.QtQuick.QSGGeometry.Point2D' object is not subscriptable

I understand that vertexDataAsPoint2D() returns only one point2D. From the documentation it should return a pointer. I am unclear how to access the other points. Please find attached my project.