[epper]

I don't think that decorators are too complex to be used usually... In python it should be a known and understood pattern and therefore it should not scare at all.

(Moreover it should handle multiple args, and there are better and more popular implementation such as @memoize)

However my assumption in this specific case is that the project is not small and therefore that decorator and this "pattern" could be used somewhere else too. If this is not the case I agree with you that it would just add too much complexity and it would hence be better to not have the decorator at all. The get_cached_user_by_username and get_cached_user_by_id would just handle the cache hit/miss by themselves.

Still it would be much more readable, because the main point I would say is to separate a long or too nested method in more methods.

    def get_cached_user_by_id(id):
        user = cache.get_user_by_id(id)
        if not user:
            user = db.get_user_by_id(id)
            cache.set_user(user)
        return user
    
    def get_cached_user_by_username(username):
        user = cache.get_user_by_username(username)
        if not user:
            user = db.get_user_by_username(username)
            cache.set_user(user)
        return user
    
    def get_cached_user(user_id = None, username = None):
        user = None
        if user_id:
            user = get_cached_user_by_id(user_id)
        else if username:
            user = get_cached_user_by_username(username)
        
        if not user:
            raise ValueError('User not found')
        
        return user

(Thanks for the .__name__ tip... I have not use python for a while)