async generator breakage

[scop]

pyupgrade 2.21.0, python 3.8.0

import asyncio


async def agen():
    for x in range(5):
        yield x


async def main():
    x = tuple([i ** 2 async for i in agen()])
    print(x)


asyncio.run(main())

$ python t2.py
(0, 1, 4, 9, 16)

pyupgrade makes this change:

--- t2.py.orig	2021-07-15 22:19:32.201257932 +0300
+++ t2.py	2021-07-15 22:23:54.089120663 +0300
@@ -10 +10 @@
-    x = tuple([i ** 2 async for i in agen()])
+    x = tuple(i ** 2 async for i in agen())

...which breaks:

$ python t2.py
Traceback (most recent call last):
  File "t2.py", line 14, in <module>
    asyncio.run(main())
[...]
    x = tuple(i ** 2 async for i in agen())
TypeError: 'async_generator' object is not iterable

[MarcoGorelli]

Thanks for the report - do you know if it's enough to just exclude list comprehensions which include async generators from the feature?

[asottile]

looks like you'd just skip if any of the generators have an is_async=1 comprehension:

$ astpretty --no-show-offsets /dev/stdin <<< 'async def f(): [1 async for x in ...]'
Module(
    body=[
        AsyncFunctionDef(
            name='f',
            args=arguments(args=[], vararg=None, kwonlyargs=[], kw_defaults=[], kwarg=None, defaults=[]),
            body=[
                Expr(
                    value=ListComp(
                        elt=Num(n=1),
                        generators=[
                            comprehension(
                                target=Name(id='x', ctx=Store()),
                                iter=Ellipsis(),
                                ifs=[],
                                is_async=1,
                            ),
                        ],
                    ),
                ),
            ],
            decorator_list=[],
            returns=None,
        ),
    ],
)