Style all symbology categories the same way in QGIS

Question

I want to be able to categorize my layer by a field called 'Location'. The sole purpose of this is to quickly be able to toggle sections of my layer on and off as I am creating multiple map figures. Only some sections of my layer are relevant for specific figures.

Is there a way to create categories that are styled the exact same way (i.e., same colour and same symbol)?

My marker is not a single colour, so making a colour ramp only with one colour (i.e., green) won't work (as it will change the white parts of my symbol to the green colour).

I also know you can use rule-based labelling, but I'm purely asking so I can have a quick solution to categorizing my layer (rather than manually changing each symbol).

Answer 1

Set the symbol and use this code to change the styling to categorized and apply the old symbol to all new categories:

#The layer name and field used to categorize
layer = QgsProject.instance().mapLayersByName("pointlayer123")[0] #Change to match your layer name
category_field = "objekttypnr" #And category field

#Find all unique values in category field
uniquevals = list({f[category_field] for f in layer.getFeatures()})

#Create a new renderer object
new_renderer = QgsCategorizedSymbolRenderer(attrName=category_field)

#Fetch the current layer symbol
oldsymbol = layer.renderer().symbol()

for val in uniquevals: #For each unique value
    qrc = QgsRendererCategory() #Create a render category object
    qrc.setLabel(str(val)) #Set the label (whats shown in layer tree)
    qrc.setValue(val) #Set the category value 
    qrc.setSymbol(oldsymbol.clone()) #Clone the old symbol
    new_renderer.addCategory(qrc) #Add the render category object to the new renderer
layer.setRenderer(new_renderer)

QgsCategorizedSymbolRenderer QgsRendererCategory

Answer 2

If you want to stick with graduated symbols, you can right click the 1st symbol, copy the style, then right click every other symbol (one by one) and paste the style.

On the other hand, you can switch to rule based symbols, which will automatically create a rule for each of the class you had in the graduated symbology. Select all rules, right click, paste symbol to set all of them at once.