Things declared at the class level are "in-scope" within a Python class

demo.py

def a_decorator_that_takes_arguments(fubar):
    def inner_decorator(func):
        nonlocal fubar
        func.thing = fubar
        return func
    return inner_decorator


class ThingUsingDecorator(object):
    
    # This object is in scope for the rest of the class declaration
    CLASS_GLOBAL = 'xyz'
    
    # So, you can use it when calling the decorator
    @a_decorator_that_takes_arguments(CLASS_GLOBAL)
    def nonsense_method(self):
        return 'abc'

# Example of use
example_thing = ThingUsingDecorator()

print(example_thing.nonsense_method())
print(example_thing.nonsense_method.thing)