I'm a Python newbie, and that code was immediately clear and obvious to me when I read it.

I won't say it would be clear anyone that reads it, because we live in a world where people who claim to be programmers can't do fizz buzz.

I'm a Python veteran, and, if you do it like this, I'll shoot you.

Add a @memoize decorator and do it there, you need to always be as obvious as possible. Compare:

    @memoize
    def fibonacci(n): pass
    
    def fibonacci(n, memory=[]): pass

You don't even need documentation for the first example.

Starting from Python 3.2 there is a builtin decorator: http://docs.python.org/dev/library/functools.html#functools....

That's fantastic, thanks for the link.

I agree with your sceptisism. This is misusing a language feature, a better approach is using a decorator.