On 06/02/14 20:40, Aseem Bansal wrote: > I read in these groups that asyncio is a great addition to Python 3. I have > looked around and saw the related PEP which is quite big BTW but couldn't > find a simple explanation for why this is such a great addition. Any simple > example where it can be used?
AFAIR, Guido's US Pycon 2013 keynote is where he introduced asyncio (or tulip, which is the "internal codename" of the project) so you can watch it to get a good idea about his motivations. So what is Asyncio? In a nutshell, Asyncio is Python's standard event loop. Next time you're going to build an async framework, you should build on it instead of reimplementing it using system calls available on the platform(s) that you're targeting, like select() or epoll(). It's great because 1) Creating an abstraction over Windows and Unix way of event-driven programming is not trivial, 2) It makes use of "yield from", a feature available in Python 3.3 and up. Using "yield from" is arguably the cleanest way of doing async as it makes async code look like blocking code which seemingly makes it easier to reason about the flow of your logic. The idea is very similar to twisted's @inlineCallbacks, if you're familiar with it. If doing lower level programming with Python is not your cup of tea, you don't really care about asyncio. You should instead wait until your favourite async framework switches to it. > It can be used to have a queue of tasks? Like threads? Maybe light weight > threads? Those were my thoughts but the library reference clearly stated that > this is single-threaded. So there should be some waiting time in between the > tasks. Then what is good? You can use it to implement a queue of (mostly i/o bound) tasks. You are not supposed to use it in cases where you'd use threads or lightweight threads (or green threads, as in gevent or stackless). Gevent is also technically async but gevent and asyncio differ in a very subtle way: Gevent does cooperative multitasking whereas Asyncio (and twisted) does event driven programming. The difference is that with asyncio, you know exactly when you're switching to another task -- only when you use "yield from". This is not always explicit with gevent, as a function that you're calling can switch to another task without letting your code know. So with gevent, you still need to take the usual precautions of multithreaded programming. Gevent actually simulates threads by doing task switching (or thread scheduling, if you will) in userspace. Here's its secret sauce: https://github.com/python-greenlet/greenlet/tree/master/platform There's some scary platform-dependent assembly code in there! I'd think twice before seriously relying on it. Event driven programming does not need such dark magic. You also don't need to be so careful in a purely event-driven setting as you know that at any point in time only one task context can be active. It's like you have an implicit, zero-overhead LOCK ALL for all nonlocal state. Of course the tradeoff is that you should carefully avoid blocking the event loop. It's not that hard once you get the hang of it :) So, I hope this answers your questions. Let me know if I missed something. Best regards, Burak -- https://mail.python.org/mailman/listinfo/python-list
