Automating classification of symbology in PyQGIS

Question

I have created this code to categorize my layer symbology based on the attribute plant_allo. However I still have to press the classify button which I also want to automate in PyQGIS. Can anyone help me with this last step?

Here is my code:

year = 2030
allocated_regions = QgsVectorLayer(output_folder + "regions_w_plant_alloc_" + str(year) + ".shp", "allocated_regions_" + str(year), "ogr")
QgsProject.instance().addMapLayer(allocated_regions)

# Field name
expression = 'plant_allo'
# Set the categorized renderer
renderer = QgsCategorizedSymbolRenderer(expression)
allocated_regions.setRenderer(renderer)
allocated_regions.triggerRepaint()

Answer 1

According to Documentation, you have to either explicitly specify category list or add later by calling addCategory().

allocated_regions = iface.activeLayer()

field_name = 'plant_allo'
field_index = allocated_regions.fields().indexFromName(field_name)
unique_values = allocated_regions.uniqueValues(field_index)

# create category list
category_list = []
for value in unique_values:
    symbol = QgsSymbol.defaultSymbol(allocated_regions.geometryType())
    category = QgsRendererCategory(value, symbol, str(value))
    category_list.append(category)

# create renderer by specifying category list
renderer = QgsCategorizedSymbolRenderer(field_name, category_list)
style = QgsStyle().defaultStyle()
ramp = style.colorRamp('Viridis')
renderer.updateColorRamp(ramp)

allocated_regions.setRenderer(renderer)
allocated_regions.triggerRepaint()