I have gone through the documentation of aiter and anext (New in version 3.10). But not understanding how to use them.

I have the following program:

import asyncio

async def get_range():
    for i in range(10):
        print(f"start {i}")
        await asyncio.sleep(1)
        print(f"end {i}")
        yield i

class AIter:
    def __init__(self, N):
        self.i = 0
        self.N = N

    def __aiter__(self):
        return self

    async def __anext__(self):
        i = self.i
        print(f"start {i}")
        await asyncio.sleep(1)
        print(f"end {i}")
        if i >= self.N:
            raise StopAsyncIteration
        self.i  = 1
        return i

async def main():
    async for p in AIter(10):
        print(f"finally {p}")

if __name__ == "__main__":
    asyncio.run(main())

How can I use aiter and anext builtin here?

CodePudding user response：

Like with the regular synchronous iter and next builtins, you rarely need to use the new builtins directly. The async for loop in main calls the __aiter__ and __anext__ methods of your class already. If that does all you want, you're home free.

You only need to explicitly use aiter and anext if you are writing code that interacts with an asynchronous iterator in some way not directly supported by a async for loop. For instance, here's an asynchronous generator that yields pairs of values from the iterable it's given:

async def pairwise(aiterable, default=None):
    ait = aiter(aiterable)                  # get a reference to the iterator
    async for x in ait:
        yield x, await anext(ait, default)  # get an extra value, yield a 2-tuple

If you loop on pairwise(AIter(10)) in your main function, you'll find that it now prints tuples of numbers, like finally (0, 1). Before each tuple, you'll see two sets of the begin and end lines printed by the iterator class, one for each value that ends up in the paired result.