How to add Callouts to labels with PyQGIS?

Question

My goal is to add Callouts (Manhattan type) to labels in a point layer with PyQGIS.

Here is what I got so far, which basically renders the labels without the callouts:

font = QgsTextFormat()
font.setFont(QFont('MS Shell Dlg 2'))
font.setSize(12)
p_layer = QgsPalLayerSettings()
p_layer.setFormat(font)
p_layer.fieldName = 'label'
p_layer.enabled = True
labels = QgsVectorLayerSimpleLabeling(p_layer)
layer.setLabeling(labels)
layer.setLabelsEnabled(True)
layer.triggerRepaint()

What I have tried:

I read in the documentation that the QgsPalLayerSettings class has a method named setCallout, which if I understand correctly, takes an object of QgsCallout class as argument.

When I try to start setting/using the QgsCallout() class, I get the following message in the QGIS Python console:

TypeError: qgis._core.QgsCallout represents a C++ abstract class and cannot be instantiated

According to this answer in StackOverflow:

"The error means there are some methods of the class that aren't implemented. ..."

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Question: How to add Callouts to labels with PyQGIS? I'm using QGIS version 3.14.1

Answer 1

You can instantiate the QgsManhattanLineCallout() class instead of the abstract parent QgsCallout() class.

Try the example code below:

layer = QgsProject().instance().mapLayersByName('Your_layer_name')[0]

txt_format = QgsTextFormat()
txt_format.setFont(QFont('MS Shell Dlg 2', 10))
txt_format.setColor(QColor('black'))

settings = QgsPalLayerSettings()
settings.setFormat(txt_format)
settings.fieldName = 'labels'
settings.drawLabels = True

callouts = QgsManhattanLineCallout()
callouts.setEnabled(True)

settings.setCallout(callouts)

labels = QgsVectorLayerSimpleLabeling(settings)
layer.setLabeling(labels)
layer.setLabelsEnabled(True)

layer.triggerRepaint()
iface.mapCanvas().refresh()

After running the script above and moving a couple of labels, the callout lines were drawn as seen below on my test layer: