PROTON-2322 Fix various flake8 warnings (manual changes)

[jiridanek]

No description provided.

[astitcher]

Remove the extra comment:
Type annotations are comments deliberately so they don't need changing fixing etc.
But my read of the doc is that this is available on 2.7 anyway.

[jiridanek]

Flake 8 looks inside # type: comments and complains if it is using something that wasn't declared; I'd leave the comment, type annotations are awesome and when Python 2.7 is dropped, they can be used more fully.

[astitcher]

The doc for mypy says that Dict is available in typing for 2.7 - not sure what's going on here, but I strongly think we should ignore or silence flake8 here.

[jiridanek]

>>> import typing
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named typing

Has to be installed with pip; it is part of stdlib only since 3.5 or maybe 3.6

[jiridanek]

and the comment I put there is silencing flake8, thats the # noqa part of it

[astitcher]

Also re type comments - I'm much more interested in typeshed (as in separate) function level type annotations - I think I put that comment there as a helpful piece of user level info to help me understand the code.
I don't think having flake8 check this is very useful tbh, so just stop it checking type annotation for the moment.
If I want type checking I'm going to use mypy

[jiridanek]

Whether flake8 runs under pyhotn2 or python3 probably plays a role here. In Python 3 code, you are supposed to have that from typing import Dict; if you forget, it's an error that flake8 can help you with.

The flake8 error this produced is

30: ./proton/_delivery.py:37:18: F821 undefined name 'Dict'

so exactly same result as if you used that name in your code. I don't see a way to tell flake8 not to behave like this, except with the # noqa comment. There is only a single type annotation like this. I strongly believe that what's in the PR is adequate until Proton moves to 3.6. Then we can simply do from typing import and we'll do type annotations the 3.x way.

[jiridanek]

One reason we may want this flake8 behavior is that it quickly finds typos in type annotations. Mypy runs significantly slower.

[astitcher]

Just add the # noqa without the extra comment then - that maintains the informal comment nature. I care much less about this sort of annotation than function level which will be useful to people using the library in an IDE

[jiridanek]

I wanted to mark the line for revisiting when we drop Python 2.7. Because then I can delete the # noqa and add from typing import Dict at the top of the file, and maybe rewrite the type annotation to PEP 526 syntax.