Asynchronous iterator & asynchronous generator & asynchronous context manager

Asynchronous iterator

Similar to iterators , Realized __aiter__() and __anext__() Method , And return to a awaitable object

obj.__aiter__(self):
    return  Asynchronous iterator 

obj.__anext__(self):
    return  Iterator next result value ,  Thrown at the end  `StopAsyncIteration`  error 

#  Example 
import asyncio

class Reader:
    def __init__(self):
        self.i = 0

    def __aiter__(self):
        return self

    async def get_next(self):
        self.i += 1
        if self.i >= 100:
            return None
        else:
            return self.i

    async def __anext__(self):
        next = await self.get_next()
        if next:
            return next
        else:
            raise StopAsyncIteration


async def main():
    # async for  It needs to be written in the coprocessor function 
    async for item in Reader():
        print(item)

asyncio.run(main())

Asynchronous context manager

Realization __aenter__() and __aexit__() The method is an asynchronous context manager

import asyncio

class AsyncContextManager:
    def __init__(self):
        self.conn = None
    
    async def __aenter__(self):
        print(' Enter the context ...')
        self.conn = await asyncio.sleep(1)
        return self

    async def __aexit__(self, exc_type, exc, tb):
        print(' Leave the context ...')
        # self.conn.close()

    async def dosomething(self):
        print(' perform xxx')
        return '666'


async def main():
    async with AsyncContextManager() as f:
        res = await f.dosomething()
        print(res)


asyncio.run(main())

Asynchronous generator

import asyncio

async def gener():
    for i in range(1, 100):
        yield i
        await asyncio.sleep(1)

async def test():
    async for item in gener():
        print(item)

async def main():
    tasks = [asyncio.create_task(test()) for _ in range(3)]
    await asyncio.wait(tasks)

asyncio.run(main())