Hi Looks like py3-attrs is now (OpenBSD 6.6 Python 3.7) a requirement for running py3-aiohttp:
km@beebox ~ $ python3.7 Python 3.7.4 (default, Aug 22 2019, 13:50:57) [Clang 8.0.0 (tags/RELEASE_800/final)] on openbsd6 Type "help", "copyright", "credits" or "license" for more information. >>> import aiohttp Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/usr/local/lib/python3.7/site-packages/aiohttp/__init__.py", line 6, in <module> from .client import ( File "/usr/local/lib/python3.7/site-packages/aiohttp/client.py", line 28, in <module> import attr ModuleNotFoundError: No module named 'attr' root@beebox ~ # pkg_add py3-attrs quirks-3.182 signed on 2019-10-12T12:14:24Z py3-attrs-18.2.0p0: ok km@beebox ~ $ python3.7 Python 3.7.4 (default, Aug 22 2019, 13:50:57) [Clang 8.0.0 (tags/RELEASE_800/final)] on openbsd6 Type "help", "copyright", "credits" or "license" for more information. >>> import aiohttp >>>