Decorators Python

Despite the many hours I spend writing python code, it's not often that I come across concepts that don't make sense. But it does happen, and one of those concepts (patterns?) is the decorator.

Blender scripting uses a class method (@classmethod) sometimes, so the notation isn't alien. Stackoverflow has an explanation that managed to finally break it down for me. Now I know from experience that with every new concept that comes into the repertoire it's likely i'll use and abuse it for a while until I can judge more sanely when to use the pattern, and when it gets in the way of readability.

I will avoid explaining here how this works, read the stackoverflow article. But as usual here is a snippet that sums up what I managed to get from it.

	def add_bold(fn):
	def perform(input_string):
	return '<b>' + fn(input_string) + '</b>'
	return perform
	@add_bold
	def regular(input_string):
	return input_string
	print(regular('chop'))

view raw for the sake.py hosted with ❤ by GitHub

..Perhaps come back to this post with more blender related reasons to use a decorator. Or if you know of a use that you would like to showcase, let me know below.

here's another:

	def mouse_change(func):
	def add_mouse_change(*args):
	print('mouse wait')
	func(*args)
	print('mouse normal')
	return add_mouse_change
	@mouse_change
	def monkey_business(a, b, c):
	print('a={0}, b={1}, c={2}'.format(a, b, b))
	monkey_business(10, 20, 30)

view raw punga.py hosted with ❤ by GitHub

or a more bpy related version:

	import bpy
	import time
	# declare the decorator
	def mouse_change(func):
	def add_mouse_change(*args):
	bpy.context.window.cursor_set("WAIT")
	func(*args)
	bpy.context.window.cursor_set("DEFAULT")
	return add_mouse_change
	class SimpleCBOperator(bpy.types.Operator):
	bl_idname = "node.some_callback_identifier"
	bl_label = "Short Name"
	# bl_options = {'REGISTER', 'UNDO'}
	fn_name = bpy.props.StringProperty(default='')
	@mouse_change
	def dispatch(self, context, type_op):
	if type_op == 'some_named_function':
	time.sleep( 5 )
	print(type_op)
	elif type_op == 'some_named_other_function':
	time.sleep( 5 )
	print(type_op)
	def execute(self, context):
	self.dispatch(context, self.fn_name)
	return {'FINISHED'}
	def register():
	bpy.utils.register_class(SimpleCBOperator)
	def unregister():
	bpy.utils.unregister_class(SimpleCBOperator)
	if __name__ == "__main__":
	register()
	# test call
	bpy.ops.node.some_callback_identifier(fn_name='some_named_function')

view raw operator_simple.py hosted with ❤ by GitHub