the sqlalchemy demo is broken with python 3.7

[albertwh1te]

        async for row in conn.execute(tbl.select()):
            print(row.id, row.val)

the sqlalchemy demo is broken with python 3.7

TypeError: 'async for' received an object from __aiter__ that does not implement __anext__: coroutine

[asvetlov]

@markwh1te sorry, your fix is incorrect.
The proper fix should drop async from def __aiter__ in cursor.py

[sc-syf]

yeah, just as @asvetlov note, with python 3.7, you should change async def __aiter__ to def __aiter__

[dnp1]

@markwh1te

If you yield values from an "async function", an AsyncGenerator is returned and everything is fine for python 3.7

But here you intend to return an object that already implements __anext__ (self), so you must drop the async from __aiter__ as pointed above.

I'm waiting for this fix, also. Are you planning to complete it or I should open my pull request?

[albertwh1te]

@dnp1 Sorry for the delay, I am pretty busy recently. I fixed this in #357.

[anyUesr]

0.0.20 do not fix this, please recheck it:

In [15]: import aiomysql                                                                                                                                                            

In [16]: aiomysql.__version__                                                                                                                                                       
Out[16]: '0.0.20'

In [17]: async def test(): 
    ...:     async with mysql_pool.acquire() as conn: 
    ...:         async for one_feature_info_res in conn.execute(FeatureInfoT.select()): 
    ...:             print(one_feature_info_res) 
    ...:                                                                                                                                                                            

In [18]: loop.run_until_complete(test())                                                                                                                                            
/home/redis/.pyenv/versions/3.7.2/bin/ipython:3: RuntimeWarning: coroutine '_SAConnectionContextManager.__aiter__' was never awaited
  # -*- coding: utf-8 -*-
RuntimeWarning: Enable tracemalloc to get the object allocation traceback
/home/redis/.pyenv/versions/3.7.2/bin/ipython:3: RuntimeWarning: coroutine 'SAConnection._execute' was never awaited
  # -*- coding: utf-8 -*-
RuntimeWarning: Enable tracemalloc to get the object allocation traceback
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-18-66585a8d0722> in <module>
----> 1 loop.run_until_complete(test())

~/.pyenv/versions/3.7.2/lib/python3.7/asyncio/base_events.py in run_until_complete(self, future)
    582             raise RuntimeError('Event loop stopped before Future completed.')
    583 
--> 584         return future.result()
    585 
    586     def stop(self):

<ipython-input-17-fa7af2a10cfe> in test()
      1 async def test():
      2     async with mysql_pool.acquire() as conn:
----> 3         async for one_feature_info_res in conn.execute(FeatureInfoT.select()):
      4             print(one_feature_info_res)
      5 

TypeError: 'async for' received an object from __aiter__ that does not implement __anext__: coroutine

[stkrp]

Hello.

I'm facing with same problem on version 0.0.20 from master branch (not PyPI). Could the following code be the cause? I use Python 3.8 in Docker.

class _SAConnectionContextManager(_ContextManager):
    async def __aiter__(self):
        result = await self._coro
        return result

https://github.com/stkrp/aiomysql/blob/b16e5bd8f31e0644d180599c87deb9ffea0c2007/aiomysql/utils.py#L73

Workaround

import asyncio

from aiomysql.sa import create_engine


async def main():
    query = "SELECT table_name FROM information_schema.tables;"

    db = await create_engine(user="root", db="db", host="mysql", password="")

    async with db.acquire() as conn:
        cursor = await conn.execute(query)
        async for row in cursor:
            print(row)


if __name__ == "__main__":
    asyncio.run(main())

UPD. I found a related issue: #410.