[Python-Dev] PEP 492: async/await in Python; version 4 (original) (raw)

Yury Selivanov yselivanov.ml at gmail.com
Fri May 1 22:06:27 CEST 2015

On 2015-05-01 3:23 PM, Yury Selivanov wrote:

Let's say it this way: I want to know what I am looking at when I browse through the code -- an asynchronous iterator, or a normal iterator. I want an explicit difference between these protocols, because they are different.

Moreover, the below code is a perfectly valid, infinite iterable: class SomeIterable: def iter(self): return self async def next(self): return 'spam' I'm strong -1 on this idea.

To further clarify on the example:

 class SomeIterable:
      def __iter__(self):
          return self
      async def __aiter__(self):
          return self
      async def __next__(self):
          print('hello')
          raise StopAsyncIteration

If you pass this to 'async for' you will get 'hello' printed and the loop will be over.

If you pass this to 'for', you will get an infinite loop, because 'next' will return a coroutine object (that has to be also awaited, but it wouldn't, because it's a plain 'for' statement).

This is something that we shouldn't let happen.

Yury

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