Updating legend for graduated symbol using PyQGIS

Question

I'm trying to programmatically modify the upper and lower range values and the label on the graduated symbol renderer of a map layer, then producing a PDF from a layout based on that map.

The map item updates correctly to reflect changes in the upper and lower range values, but the legend item does not reflect changes I make to the labels.

I've tried all the triggerRepaint(), update(), legendUpdate(), etc. calls I could find but the only thing I found that made the legend update was setAutoUpdateModel(True), which has the unfortunate side-effect of making the legend include all the layers that I don't want to see a legend for. I'd even use that as a work-around if I could figure out how to programmatically hide the legend items I don't want.

What might I be missing or doing wrong?

Answer 1

I faced the same when did a standalone script for generating layouts and images from there. Modern pyqgis syntax may require resetting the whole symbology object. This was my case with classification method:

# define layer and its renderer
layer = iface.activeLayer()
renderer = layer.renderer()

# setting the classification method 
method = QgsClassificationEqualInterval()
method.setLabelPrecision(0)
method.setLabelFormat('%1 to %2')
renderer.setClassificationMethod(method)

renderer.updateClasses(layer_out, 5) # let there be five classes

# updating layer symbology, changes will be seen immediately in layout window
renderer.updateColorRamp()
renderer.updateRangeLabels()
layer.setRenderer(renderer)
layer.triggerRepaint()
layer.reload() 

# and one more optional method that I used before to see changes in layer treeview
iface.layerTreeView().refreshLayerSymbology(layer.id())

Other methods are listed here: https://api.qgis.org/api/qgsclassificationmethod_8h_source.html#l00092 and in another QGIS source code documentations