CircleCI: Run some key flake8 tests

[cclauss]

These tests find Python syntax errors and undefined names.
(A second attempt at #63)

[cclauss]

Does not kick off a CircleCI build. :-(

Check the setting at https://circleci.com/gh/my8100/scrapydweb/edit

[my8100]

Does not kick off a CircleCI build. :-(

Check the setting at https://circleci.com/gh/my8100/scrapydweb/edit

I just found that "Build forked pull requests" is off by default.
Sorry for the inconvenience.

[my8100]

Could you push again?

[cclauss]

Yeah!!

[my8100]

You have to pull my previous commit 1ea0ab3 first
in order to get all the tests to pass.

[my8100]

BTW, don't forget to rollback your change in README.md.

[cclauss]

I liked my change to README.md

[coveralls]

Pull Request Test Coverage Report for Build 37

• 2 of 4 (50.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 88.879%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
scrapydweb/views/myview.py	1	2	50.0%
scrapydweb/views/operations/deploy.py	1	2	50.0%

Totals
Change from base Build 25:	0.2%
Covered Lines:	3149
Relevant Lines:	3543

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 36

• 2 of 4 (50.0%) changed or added relevant lines in 2 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.3%) to 88.936%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
scrapydweb/views/myview.py	1	2	50.0%
scrapydweb/views/operations/deploy.py	1	2	50.0%

Files with Coverage Reduction	New Missed Lines	%
scrapydweb/views/overview/jobs.py	2	93.46%

Totals
Change from base Build 25:	0.3%
Covered Lines:	3151
Relevant Lines:	3543

---

💛 - Coveralls

[my8100]

Details on --select=E9,F63,F7,F82: deeppavlov/DeepPavlov#913 (comment)

flake8 . --count --exclude=./venv* --select=E9,F63,F7,F82 --show-source --statistics

On the flake8 test selection, this PR does not focus on "style violations" (the majority of flake8 error codes that python/black can autocorrect). Instead these tests are focus on runtime safety and correctness:

• E9 tests are about Python syntax errors usually raised because flake8 can not build an Abstract Syntax Tree (AST). Often these issues are a sign of unused code or code that has not been ported to Python 3. These would be compile-time errors in a compiled language but in a dynamic language like Python they result in the script halting/crashing on the user.
• F63 tests are usually about the confusion between identity and equality in Python. Use ==/!= to compare str, bytes, and int literals is the classic case. These are areas where a == b is True but a is b is False (or vice versa).
• F7 tests logic errors and syntax errors in type hints
• F82 tests are almost always undefined names which are usually a sign of a typo, missing imports, or code that has not been ported to Python 3. These also would be compile-time errors in a compiled language but in Python a NameError is raised which will halt/crash the script on the user.