Understanding of @gen.coroutine annotation

Question

I know that my question looks to broad, but I hope the answer on this question will give me correct direction what to read on. I am new to Tornado framework, basically I am new to Python. I am looking into this project: Could you please explain me a few lines of code:

@gen.coroutine
def get_me(self):
    raise gen.Return((yield self._api.get_me()))

• What @gen.coroutine annotation is for?
• raise keyword is used for exceptions, isn't it? Why we use it here?
• Why we return everything in form of generator. Is the concept of Tornado framework to use generators. What is the reason?

Answer 1

• @gen is a decorator, it will modify the function below it at definition.
• It uses raise to return values and will catch it with except gen.Return (I find it ugly but it works).
• Generators are a convinient way to avoid memory usage and allow lazy programing, always try to return a generator over an iterator.