💡 Summary: Python’s
__aenter__() magic method is semantically identical to
__enter__() but is used for asynchronous and parallel programming. Python calls the
__aenter__() magic method when starting an
async with block whereas the
__aexit__() method is called when leaving it. An object that implements both
__aexit__() methods is called an asynchronous context manager.
import asyncio class MyAsyncContextManager: async def __aenter__(self): print("ENTER async with") async def __aexit__(self, *args): print("EXIT async with") async def run(): async with MyAsyncContextManager() as cm: print("BODY async with") asyncio.get_event_loop().run_until_complete(run())
ENTER async with BODY async with EXIT async with
- We define a custom class
MyAsyncContextManagerthat defines the
__aexit__()magic methods to make it an asynchronous context manager, i.e., allowing it to be used in an
- You define an asynchronous function
run()that holds the asynchronous
withenvironment and run it using the
asyncio.get_event_loop().run_until_complete()function. The reason for this is that you need to use the async with block within an asynchronous function (using the expression
async defto define it).
We call this a “Dunder Method” for “Double Underscore Method” (also called “magic method”). To get a list of all dunder methods with explanation, check out our dunder cheat sheet article on this blog.
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