STYLE: support flake8>3.4.1

[jreback]

flake8 > 3.4.1 has a fair amount more warnings

we need to either fix our code or remove the warnings

example from: https://travis-ci.org/pandas-dev/pandas/jobs/305553688

note that #18418 will pin 3.4.1, so these won't show in the CI.
We will need to revert this commit once things are fixed.

prob ok to turn off E740 (though fixing is not a big deal)
should fix the E722

$ ci/lint.sh
inside ci/lint.sh
Linting *.py
pandas/compat/pickle_compat.py:36:13: E722 do not use bare except'
pandas/compat/pickle_compat.py:47:13: E722 do not use bare except'
pandas/compat/pickle_compat.py:171:1: E722 do not use bare except'
pandas/compat/pickle_compat.py:199:5: E722 do not use bare except'
pandas/core/categorical.py:601:9: E722 do not use bare except'
pandas/core/common.py:571:5: E722 do not use bare except'
pandas/core/common.py:589:5: E722 do not use bare except'
pandas/core/common.py:608:5: E722 do not use bare except'
pandas/core/common.py:620:5: E722 do not use bare except'
pandas/core/frame.py:2118:9: E722 do not use bare except'
pandas/core/frame.py:2561:13: E722 do not use bare except'
pandas/core/frame.py:5717:21: E722 do not use bare except'
pandas/core/frame.py:6232:9: E722 do not use bare except'
pandas/core/indexing.py:136:13: E722 do not use bare except'
pandas/core/indexing.py:540:17: E741 ambiguous variable name 'l'
pandas/core/indexing.py:698:21: E741 ambiguous variable name 'l'

[AaronCritchley]

On the E722 errors, are you happy if they're modified to except Exception? Or preferred to explicitly catch Exceptions we're expecting?

Happy to fix the E741 issues too

[jreback]

would really like to be explicit on exceptions and put what is actually thrown rather than Exception

[tzyl]

Hey @jreback, is this still open? When running the ci/lint.sh script locally with flake8@3.5.0 I see E722 errors only. Happy to take a look at this if you still want this to be done.

[WillAyd]

@tzyl still open - PRs are welcome

[AaronCritchley]

Working on this now, will hopefully have done by tomorrow but there are lots of E722 issues. I'm making some (not so) educated guesses on expected exceptions, but where I can't derive the original intent / logic I'm just changing to except Exception, happy for these cases to be changed when it comes to reviewing the PR if someone else can make an informed guess.

Sorry for going quiet on this back in Dec, not sure what happened, my bad!