wtf.py

async def f():
    return ValueError()

async def g():
    try:
        raise KeyError
    except:
        value_error = await f()
        # This prints: KeyError() in CPython 3.5, 3.6, current master
        # Apparently returning an exception object from an async function triggers
        # implicit exception chaining?!
        print(repr(value_error.__context__))

try:
    g().send(None)
except StopIteration:
    pass