How to use the array_length() field calculator expression in PyQGIS

Question

How can I use this field calculator expression in PyQGIS? Right now i have the following code. It generates a new field but it does not fill the field. (see bottom for layer example)

layer = iface.activeLayer()

pv = layer.dataProvider()
pv.addAttributes([QgsField('Count', QVariant.Double)])

layer.updateFields()

expression1 = QgsExpression('array_length(overlay_nearest(PND_Aangrenzend,"",limit:=10,max_distance:=5))')

context = QgsExpressionContext()
context.appendScopes(QgsExpressionContextUtils.globalProjectLayerScopes(layer))

with edit(layer):
    for f in layer.getFeatures():
        context.setFeature(f)
        f['Count'] = expression1.evaluate(context)
        layer.updateFeature(f)

Answer 1

I am not sure what the wider context of your question is, but you can use expressions in QGIS like so:

layer.selectByExpression(expression)

This may mean that you can use your expression like so:

layerName = "layerNameGoesHere"
layer = QgsProject.instance().mapLayersByName(layerName)[0]
expression = f'array_length(overlay_nearest( @layer ,"",limit:=10,max_distance:=5))'
layer.selectByExpression(expression)