Hydrotools nwis-client requires python 3.7

[hellkite500]

The hydrotools nwis-client requires a minimum python version of 3.7. This means hypy needs to document a similar minimum version.

Current behavior

With latest version of hydrotools, hypy nwislocation doesn't work with python 3.6.

Steps to replicate behavior (include URLs)

Try running unit tests with python 3.6

[aaraney]

This is because of the usage of aiohttp-client-cache. See here specifically for the downstream issue. At the surface level, it seems that the issue is just with aiohttp-client-cache's use of type hint features added in py37. It may be worth exploring this to see about a potential way around this and opening a PR there to lower the version requirement.

[aaraney]

It's probably in our best interest to move to python 3.7 or greater as an organization. Python 3.6 will reach EOL this December.

[JWCook]

@aaraney Python 3.7 contains a large number of asyncio-specific improvements: https://docs.python.org/3/whatsnew/3.7.html#whatsnew37-asyncio

So it's highly recommended to use 3.7+ for async applications. It might be possible to make aiohttp-client-cache compatible with 3.6, but like you mentioned it will be EOL soon.