async — Expert Examples

Declares an asynchronous coroutine function or context manager

EasyIntermediateAdvancedExpert

Async internals: coroutine objects

Examining async functions under the hood.

python
import asyncio
import inspect
import dis

async def example():
    await asyncio.sleep(0)
    return 42

# Coroutine object
coro = example()
print(f"Type: {type(coro)}")
print(f"Is coroutine: {inspect.iscoroutine(coro)}")
print(f"State: {inspect.getcoroutinestate(coro)}")

# Must close or run it
coro.close()

# Bytecode
print(f"\nBytecode:")
dis.dis(example)

# async def compiles similarly to regular def
# but the code object has CO_COROUTINE flag
print(f"\nFlags: {example.__code__.co_flags}")
print(f"Is coroutine func: {inspect.iscoroutinefunction(example)}")

async def sets the CO_COROUTINE flag on the code object. The bytecode uses GET_AWAITABLE and SEND to implement await. Coroutine objects track their state (created, running, suspended, closed).

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