Fix legacy __aiter__ methods

[Askaholic]

This allows the async for syntax to be used with ResultProxy and Cursor objects in python 3.7.

Fixes #394
Fixes #386
Fixes #317

[codecov]

Codecov Report

Merging #403 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master     #403   +/-   ##
=======================================
  Coverage   92.28%   92.28%           
=======================================
  Files           9        9           
  Lines        1180     1180           
  Branches      172      172           
=======================================
  Hits         1089     1089           
  Misses         64       64           
  Partials       27       27

Impacted Files	Coverage Δ
aiomysql/sa/result.py	92% <100%> (ø)	⬆️

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[terricain]

@thehesiod thoughts on this, looks fine to me.

[thehesiod]

@terrycain aiohttp moved to 3.5.3+ to avoid this, should this lib as well?

[terricain]

Yeah I see no issue moving it to 3.5.3+ @jettify any objections?

[Askaholic]

Supporting only 3.5.3+ would make the fix even easier. Just let me know

[asvetlov]

Pretty sure @jettify has no objections :)

Side note: after sadly delaying aiohttp new release (totally my fault, my spare time is very limited now) I started to cut-off Python 3.5 in aiohttp 4.0 entirely.
I'm still extremely busy by working on asyncio for Python 3.8.
So aiohttp 4.0 has a chance to be released in August or September. The major release is a chance to change API significantly, a lot to do.
Perhaps aiomysql should sit on 3.5.3 though: new version can be published quickly.

For me the main indicator is Debian 10.

[Askaholic]

Why does SAConnectionContextManager have an __aiter__ method? Does this need to be changed to a regular function as well?

aiomysql/aiomysql/utils.py

Line 72 in 131fb9f

class _SAConnectionContextManager(_ContextManager):

[terricain]

Supporting 3.5.3+ i think would make sense for now, not sure on our 3.5 userbase but < 3.5.3 was fraught with issues.

@Askaholic you mind updating the setup.py to mandate 3.5.3+ ?

[Askaholic]

@terrycain The setup.py already does this: https://github.com/aio-libs/aiomysql/blob/master/setup.py#L13

aiomysql/setup.py

Line 13 in 131fb9f

raise RuntimeError("aiomysql doesn't support Python earlier than 3.5.3")

[jaggerwang]

@terrycain It has been three months passed, when this fix will publish to pip?

[Askaholic]

@jaggerwang If you are really desperate, you can try installing directly from git: https://stackoverflow.com/questions/20101834/pip-install-from-git-repo-branch

[jaggerwang]

@Askaholic Thanks! But this way is not so good, I choose waiting... The last update of the pip package is still at 2018:(