# how to duplicate or clone a map layer
# renaming the map layer and setting a filter
# and also setting a variable on a layer for use in scripts
# also shows how to connnect a .qml to a map layer

# Select a layer that is already added to the interface
layer_original = QgsProject.instance().mapLayersByName('original')[0]

# duplicate or clone the layer
layer_cloned = layer_original.clone()

# add it to the map
QgsProject.instance().addMapLayer(layer_cloned)

# set a name for the duplicate layer
layer_cloned.setName('layer_cloned')

# set a layer filter, in this case to just a parent table id
layer_cloned.setSubsetString("parent_id = 42")

# load a custom .qml for styling, forms, etc....
layer_cloned.loadNamedStyle('my_path/layer_style.qml')

# set a variable that would become the parent id, could be used as default value when creating a new record
QgsExpressionContextUtils.setLayerVariable(layer_cloned,'parent_id', 42)