Create ranged sub-symbology within categorized layers

Question

I am developing a plugin in PyQGIS 3. Within this plugin, I already succeeded in categorizing using PYQGIS 3 but I am still looking to find a way to create ranges within these newly created categories using PYQGIS 3. This is my code so far:

layer = QgsVectorLayer(output_folder + layer + '.shp', "layer", "ogr")
QgsProject.instance().addMapLayer(Regional_BC)

field_name = 'CNTR_CODE'
field_index = layer.fields().indexFromName(field_name)
unique_values = layer.uniqueValues(field_index)

# create category list
category_list = []
for value in unique_values:
    symbol = QgsSymbol.defaultSymbol(Regional_BC.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('RdYlGn')
renderer.updateColorRamp(ramp)

layer.setRenderer(renderer)
layer.triggerRepaint()

I want to categorize based on the column CNTR_CODE in PyQGIS 3. This step has been done in the first section of the code. However, when I want to give these produced categories sublayers color based on the fieldName 'INCOMING_T'. This is a link to the working manual flow (OPTION 1 ANSWER): Using graduate and categorize in QGIS?

I am trying to recreate the steps in the link --> option 1 answer within the PYQGIS 3 environment

Answer 1

I found the solution to this question after I took a good look at the existing documentation. Steps that need to be conducted:

1. Create CategorizedRenderer
2. Update existing CategorizedRenderer and change it into RuleBasedRenderer
3. Build a for loop that goes through all the symbologies (in my case symbologies of countries) using the ruleRend.refineRuleRanges() function.

Here is an example of what my code looks like:

#create regional_BC_year layer with symbology
layer3 = QgsVectorLayer(output_folder + 'Regional_BC_Joined_' + str(year) + '.shp', "Regional_BC_produced_" + str(year), "ogr")

# read correct field name in regional_bc layer
field_name = 'CNTR_CODE'
field_index = layer3.fields().indexFromName(field_name)
unique_values = layer3.uniqueValues(field_index)

# create category list
category_list = []
for value in unique_values:
    symbol = QgsSymbol.defaultSymbol(layer3.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('RdYlGn')
renderer.updateColorRamp(ramp)

# set new renderer of layer
layer3.crs = {'init' :'epsg:4326'}
layer3.setRenderer(renderer)
layer3.triggerRepaint()

# change to from categorizedrenderer into rulebased renderer
if renderer.type() == 'categorizedSymbol':
    ruleRend = QgsRuleBasedRenderer.convertFromRenderer(renderer)

# add layer to map and set new rulebased renderer
QgsProject.instance().addMapLayer(layer3)
layer3.setRenderer(ruleRend)
layer3.triggerRepaint()
# refresh symbology of layer
iface.layerTreeView().refreshLayerSymbology(layer3.id())

# load values of BC_per_reg column and add to vals df
vals = []
fld = 'BC_per_reg'
for f in layer3.getFeatures():
    vals.append(f[fld])

# colors of series that will be visualized
colors = ['#f7fcf5', '#d5efcf', '#9ed898', '#54b567', '#1d8641']

# calculate upper and lower values of vals df
vals = list(filter(None, vals))
vals = [float(s) for s in vals]
lower = 0.001
upper = 15

# add bounds and colors to each range and add to each "symbol"
step = 2
range_list = []
for c in colors:
    cat = [lower, lower+step, c]
    sym = QgsSymbol.defaultSymbol(layer3.geometryType())
    sym.setColor(QColor(cat[2]))
    rng = QgsRendererRange(cat[0], cat[1], sym, '{0:.1f}-{1:.1f}'.format(cat[0], cat[1]))
    range_list.append(rng)
    lower = (lower+step)

# add all symbols, and add to range_list
symbol = QgsSymbol.defaultSymbol(layer3.geometryType())
symbol.setColor(QColor('#00441b'))
rng1 = QgsRendererRange(10, 100, symbol, '{0:.1f}-{1:.1f}'.format(10, 100))
range_list.append(rng1)

# refineRuleRanges so that for eacht class --> e.g. France we will get 5 ranges of values inside
# Scale symbol based on column
if ruleRend.type() == 'RuleRenderer':
    for i in range(len(ruleRend.rootRule().children())):
        ruleRend.refineRuleRanges(layer3.renderer().rootRule().children()[i], QgsGraduatedSymbolRenderer(fld, range_list)) #inputs for QgsGraduatedSymbolRenderer(fld, range_list)

v1 = layer3

# set renderer and reload layers on map
QgsProject.instance().addMapLayer(v1)
v1.setRenderer(ruleRend)
v1.triggerRepaint()
iface.layerTreeView().refreshLayerSymbology(v1.id())

A visual representation of what the results look like:

I can now check and uncheck all countries while the ranges are visible for other countries! See unchecked regions Portugal: