Getting labeling field in variable and changing labeling field with PyQGIS

Question

I working with QGIS 3.20. I want to write a PyQGIS script to automate switching the field used for labeling in numerous layers. Currently the layers are labeled from values of a field that is different for each layer.

I thought I will follow this procedure:

1. Get the field name that is currently used for labeling (say field "X") in a variable
2. Add a new field "Label" and populate its values according to the values in field "X"
3. Set the labeling field to the "Label" field

I know how to do number 2 and I am looking for a way to do number 1 and 3. So my questions are: how do I get the labeling field name (to store in a variable)? How do I change the labeling field?

In the UI this is the labeling field I want to access and change (however its name is different for each layer):

What would be the way to go?

Answer 1

My answer is based on two answers :

Getting label feature with PyQGIS? from Leo Cardona for step 1

QgsPalLayerSettings error from ndawson for step 3

This is the code used for step 1 and step 3 :

layer = iface.activeLayer()    
# STEP 1
labeling = layer.labeling()
palyr = labeling.settings()
currently_used_field_name = palyr.fieldName
print (currently_used_field_name)
# this will print : X

#STEP 3
new_label_field = "Label"
label_settings = QgsPalLayerSettings()
label_settings.drawLabels = True
label_settings.fieldName = new_label_field
layer.setLabeling(QgsVectorLayerSimpleLabeling(label_settings))
layer.triggerRepaint()