It's absolutely baffling that an article called demystifying decorators does not actually describe decorators at all, preferring to keep them a mystery. Decorators are nothing more than a special syntax for calling a function, the meat of which can easily be explained in a single paragraph including a supporting example.

outside of __init__, I thought it wasn't the pythonic way to directly invoke double underscore functions like closure? I recall reading that you should implement a class that overrides/implements such functions instead? I get why the author might be doing it this way to describe the topic of the post, but would calling __closure__() be acceptable in production code?

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I'm not sure who this article is for, but I think it doesn't strike at the heart of the topic.

Half of the article is devoted to closures, but closures aren't essential for decorators. And the __closure__ attribute is an implementation detail that is really irrelevant. (For comparison, JavaScript has closures just like Python, but it doesn't expose the closed-over variables explicitly the way Python does.)

Decorators are simply higher order functions that are used to wrap functions. The syntax is a little funky, but all you need to know is that code like:

   @foo
   @bar
   def baz(args):
       return quux(args)

   baz = foo(bar(lambda args: quux(args))

Then there are seemingly more complex expressions like:

    @foo(42, 'blub')
    def bar(..): ...

    def foo(i, s):
        def decorator(f):
            def invoke(*args, **kwargs):
                print('decorator', i, s)
                f(*args, **kwargs)
                print('done')
        return invoke
    return decorator

    @foo(42, 'blub')
    def hello():
        print('Hello, world!')

    hello()

    # prints:
    #    decorator 42 blub
    #    Hello, world!
    #    done

And yes, these examples use closures, which are very convenient when implementing decorators. But they aren't essential. It's perfectly possible to declare a decorator this way:

    class Invoker:
        def __init__(self, f):
            self.f = f
    
        def __call__(self):
            print('before call')
            self.f()
            print('after call')
    
    def decorator(f):
        return Invoker(f)
        
    @decorator
    def hello():
        print('Hello, world!')

    hello()
    # prints:
    #     before call
    #     Hello, world!
    #     after call

The key point in all these examples is that functions in Python are first-class objects that can be referenced by value, invoked dynamically, passed as arguments to functions, and returned from functions. Once you understand that, it's pretty clear that a decorator is simply a wrapper that takes a function argument and returns a new function to replace it, usually adding some behavior around the original function.