Async Generators

Introduction

Async generators combine async functions with generator capabilities, allowing iteration over asynchronous data sources with async for.

Basic Async Generator

async def async_range(start, stop):
    for i in range(start, stop):
        await asyncio.sleep(0.1)  # Simulate async operation
        yield i

async def main():
    async for num in async_range(0, 5):
        print(f"Got: {num}")

asyncio.run(main())

Async Generator Pipeline

async def produce():
    for i in range(10):
        await asyncio.sleep(0.1)
        yield i

async def transform(item):
    await asyncio.sleep(0.1)
    return item * 2

async def consume():
    async for item in produce():
        result = await transform(item)
        print(f"Processed: {result}")

asyncio.run(consume())

Async Iterator Protocol

class AsyncCounter:
    def __init__(self, limit):
        self.limit = limit
        self.current = 0
    
    def __aiter__(self):
        return self
    
    async def __anext__(self):
        if self.current >= self.limit:
            raise StopAsyncIteration
        value = self.current
        self.current += 1
        await asyncio.sleep(0.1)
        return value

async def main():
    async for i in AsyncCounter(5):
        print(i)

asyncio.run(main())

aclose and athrow

async def async_gen():
    try:
        for i in range(10):
            yield i
    except asyncio.CancelledError:
        print("Generator cancelled")
        raise

async def main():
    ag = async_gen()
    async for i in ag:
        print(i)
        if i == 5:
            await ag.aclose()

asyncio.run(main())

Async Generator with send

async def async_gen_with_send():
    value = None
    while True:
        received = yield value
        value = received * 2 if received else 0

async def main():
    gen = async_gen_with_send()
    await gen.asend(None)  # Prime
    print(await gen.asend(5))  # 10
    print(await gen.asend(3))  # 6

asyncio.run(main())

Practice Problems

1. Create async generator for streaming data
2. Build async generator pipeline
3. Implement async iterator class
4. Handle cancellation properly
5. Use asend with async generators