Blender Add-on

To preface this post, I’ll assume you are familiar with Python and have a grasp of Blender. We’ll be using Blender 4.1, how ever other versions should work too. We’ll look into the Blender API and create a simple addon with UI.

So, what’s an addon?

Well, simply put, an add-on is a Python module that allows you to extend the functionality of Blender. For Blender to recognize a plugin, we need to define three requirements. Firstly, bl_info, stores add-on metadata, such as the name and minimum supported Blender version. Secondly, we need to implement register() and unregister() methods.

bl_info = {
	"name": "My add-on",
	"blender": (2, 80, 0),
	"category": "Object",
}
def register():
	print("Hello")
def unregister():
	print("Bye")

An astute reader may notice that this add-on doesn’t yet use Blender API functions, so let’s change that!

Your first addon

Let’s start simply, we’ll delete the default cube. To achieve this, we’ll import the Blender API and register a new operator. Operators allow us to define actions that can be executed from a menu, buttons, or a keyboard shortcut.

bl_info = {
	"name": "Remove default cube",
	"blender": (2, 80, 0),
	"category": "Object",
}

import bpy

class RemoveDefaultCube(bpy.types.Operator):
	"""Removes the pesky default cube"""		# The tooltip used in menus and buttons
	bl_idname = "object.remove_cube"		# A unique identifier for buttons and menu items to reference
	bl_label = "Remove default cube"		# The display name in the interface
	bl_options = {'REGISTER', 'UNDO'}		# Allow undo operator

	def execute(self, context):			# Implicitely called when running the operator
		objects = bpy.data.objects		# Get all objects in Blender save file
		objects.remove(objects["Cube"])		# Deletes the cube (assuming it exits)

def menu_function(self, context):
	self.layout.operator(RemoveDefaultCube.bl_idname)

def register():						# Called when the add-on is enabled
	bpy.utils.register_class(RemoveDefaultCube)
	bpy.types.VIEW3D_MT_object.append(menu_function)	# We add the operator to the 

def unregister():					# Called when the add-on is disabled
	bpy.utils.unregister_class(RemoveDefaultCube)

if __name__ == "__main__":				# Entry point for the Belnder script editor to use
	register()

After we press the play button in the text editor window in Blender, the add-on is ready to be tested. It can be found in the Object menu in the 3D viewport, or alternatively, it can be searched by typing the phrase Remove default cube.

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