Using QGIS default Random Color Ramp in Categorized symbology using PyQGIS

Question

Based on this code below, is it possible to use Random Color option in Symbology?

layer = iface.activeLayer()

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

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

renderer = QgsCategorizedSymbolRenderer(field_name, category_list)
style = QgsStyle().defaultStyle()
ramp = style.colorRamp('Greens')
renderer.updateColorRamp(ramp)

layer.setRenderer(renderer)
layer.triggerRepaint()

In this case I'm using 'Greens' color ramp, but I'd like to set "Random colors' as this "Color ramp" UI option.

Answer 1

It's absolutely possible! Just use:

renderer.updateColorRamp(QgsRandomColorRamp())

I modified your script only very slightly:

layer = iface.activeLayer()

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

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

renderer = QgsCategorizedSymbolRenderer(field_name, category_list)
renderer.updateColorRamp(QgsRandomColorRamp())
layer.setRenderer(renderer)
layer.triggerRepaint()

See results on a test layer below (I changed only the field name to 'reg_code_8'.

Before:

After:

Incidently, because random colors are the default for the categorized renderer, you don't even need to update the color ramp. You can just use:

layer = iface.activeLayer()

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

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

renderer = QgsCategorizedSymbolRenderer(field_name, category_list)
layer.setRenderer(renderer)
layer.triggerRepaint()

It will give you random colors. However, interestingly I notice that the resulting palette is consistently a bit different (colors are not as 'vibrant'). An example: